Grundig AM/FM portable "Transistor 305" troubleshooting

[Winston]

Sylvia Else wrote:

On 7/03/2012 1:46 AM, Winston wrote:
Sylvia Else wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

(...)

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

Voltage readingso
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny

(...)

As Frank observes, if the 1.4 St1 connections are compromised, then the bias for the AF124 would be affected, and on the
OP's readings, it is not.

Now, we don't know the nature of the link between that diode and pin ten of F IV, and I've seen Grundig do some rather
questionable things, but if it's just a circuit board track, the fault pretty much has to lie either in the pin 10
soldering, or in the track itself.

Good point.

I look forward to what Lenny eventually discovers.

Given the history of the radio, a cracked trace
would not be out of the question.

It'll be amusing if it was C4 or C38 or R22 that was
intermittently shorting, instead.

--Winston

 

[Sylvia Else]

On 7/03/2012 11:41 AM, Winston wrote:

Sylvia Else wrote:
On 7/03/2012 1:46 AM, Winston wrote:
Sylvia Else wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

(...)

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

Voltage readingso
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny

(...)

As Frank observes, if the 1.4 St1 connections are compromised, then
the bias for the AF124 would be affected, and on the
OP's readings, it is not.

Now, we don't know the nature of the link between that diode and pin
ten of F IV, and I've seen Grundig do some rather
questionable things, but if it's just a circuit board track, the fault
pretty much has to lie either in the pin 10
soldering, or in the track itself.

Good point.

I look forward to what Lenny eventually discovers.

Given the history of the radio, a cracked trace
would not be out of the question.

It'll be amusing if it was C4 or C38 or R22 that was
intermittently shorting, instead.

I don't think those could cause the observed effects - they'd all pull
the transistor base down to -9V, near enough.

Sylvia.

 

[Winston]

Sylvia Else wrote:

On 7/03/2012 11:41 AM, Winston wrote:
Sylvia Else wrote:
On 7/03/2012 1:46 AM, Winston wrote:
Sylvia Else wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

(...)

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

Voltage readingso
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny

(...)

As Frank observes, if the 1.4 St1 connections are compromised, then
the bias for the AF124 would be affected, and on the
OP's readings, it is not.

Now, we don't know the nature of the link between that diode and pin
ten of F IV, and I've seen Grundig do some rather
questionable things, but if it's just a circuit board track, the fault
pretty much has to lie either in the pin 10
soldering, or in the track itself.

Good point.

I look forward to what Lenny eventually discovers.

Given the history of the radio, a cracked trace
would not be out of the question.

It'll be amusing if it was C4 or C38 or R22 that was
intermittently shorting, instead.

I don't think those could cause the observed effects - they'd all pull the transistor base down to -9V, near enough.

I hope Lenny will get back to us with his findings.



--Winston

 

[Winston]

klem kedidelhopper wrote:

(...)

I didn't get to work on the radio today and probably won't be able to
tomorrow either as work, (the kind you get paid for) has to take
precedence over my hobby. Although my "hobby" as of late has seemed to
be more like my nemesis to be exact. Thanks once again for all your
input. Lenny

Did you happen to re-solder F IV pin 10 and
inspect the associated trace, Lenny?

I think Sylvia made a good point about it.

It would be hugely amusing to measure the voltage dropped
across R21 and R28 during functional / non-functional
circumstances. You could use them as current sense resistors
to point you in the direction of the open or short.

--Winston

 

[klem kedidelhopper]

On Mar 7, 12:06 am, Winston <Wins...@Bigbrother.net> wrote:

Sylvia Else wrote:
On 7/03/2012 11:41 AM, Winston wrote:
Sylvia Else wrote:
On 7/03/2012 1:46 AM, Winston wrote:
Sylvia Else wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

(...)

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

Voltage readingso
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny

(...)

As Frank observes, if the 1.4 St1 connections are compromised, then
the bias for the AF124 would be affected, and on the
OP's readings, it is not.

Now, we don't know the nature of the link between that diode and pin
ten of F IV, and I've seen Grundig do some rather
questionable things, but if it's just a circuit board track, the fault
pretty much has to lie either in the pin 10
soldering, or in the track itself.

Good point.

I look forward to what Lenny eventually discovers.

Given the history of the radio, a cracked trace
would not be out of the question.

It'll be amusing if it was C4 or C38 or R22 that was
intermittently shorting, instead.

I don't think those could cause the observed effects - they'd all pull the transistor base down to -9V, near enough.

I hope Lenny will get back to us with his findings.



--Winston

First of all let me say thank you to everyone who has become involved
in my problem. It really is so nice to be a part of this community of
kind people who are willing to help one another. I truly appreciate
all your opinions and all the advice you've sent my way.

I have been working on this radio off and on since I posted this. This
morning the alarm clock (bedroom radio) went off at 5:45 as it does
every morning with soft classical music. As we gently awoke I looked
over and saw that it was the Grundig on my bench! It was FIXED and it
was WORKING! Imagine my big let down upon actually waking up a few
minutes later and realizing that I really was in my bed, I wasn't in
the shop, and it WASN'T the Grundig, GAH! This thing isn't driving me
insane, I think it already has. Now it's haunting my nights as well as
my days....

I would have agreed that the direct relationship between the time the
radio is unpowered to the time it stays on the next time it is powered
up would definitely point to an electrolytic, but so far I have not
found it. There actually aren't that many in the signal circuit. I did
replace C 44, not because it checked bad, but because it was
suggested. However replacing it had no affect. I monitored the 1.4V
zener during intermittent periods of go/no go and the voltage remained
at 1,4V. Eventually the radio quit completely for a spell and I
bridged the following resistors: R4, R5, R29, R27, R24, R26, R25, and
then after measuring the resistance of R22, in circuit, (it was 13K),
I bridged it with a 100K (not a conclusive test I know) but just to
see if there were any affect There was none. I did resolder R22 but
that was not it either. The voltage across R22 does fluctuate quite a
bit during intermittent periods but it is a large resistor so I would
expect that. However I'm not sure if 13K is whats in parallel with R22
and R22 is really open. I thought of pulling it but first I think that
I have an idea.

Since the voltage never was exactly where it should have been, (1.18V)
upon powering the radio on the next time I think I' ll see if I can
set Vr124 to exactly 1.18V and wait and see if that might make a
difference. For one thing it will prove if R22 is working at all, and
also if the bias point is that critical to turning these transistors
on when they shouldn't be on.
I 'm also starting to wonder about the small capacitors among these
resistors that have these voltage changes about them. I really hate to
just start replacing things but I don't see any other way at this
point. I wish there were a way to isolate the offending stage, but
with the voltage changing as it is I don't see how I would do that. I
think I've ruled out the above resistors but I'll have to start
somewhere. It also frustrates me that I can't get on the collector of
AF126II because it's inside a can, (FIV) and the can is soldered onto
the board. There is another electrolytic, (C4) inside FIV but I don't
think that is part of this.

Other than that there are the small caps in and around these two
circuits and of course the ones in the last IF can (FIII) and the
detector, (FIV). I tried small spot cold spraying again around the
suspect area and even into the IF cans and detector assembly, and that
yielded nothing. I'm pretty sure I've ruled out a mechanical
intermittent also. This definitely appears to be something breaking
down electrically. I'm also wondering about one of the IF cans,
(coils) opening up intermittently. Does anyone remember how the old
five tube radios would crackle when the IF cans failed in them. I
never really knew how the cans were failing. We just replaced them and
that fixed the crackling. It occurred to me that if either coil in the
can in this radio opened up it would affect both AM and FM. I don't
recall if I mentioned it too but all the transistor can connections
have been lifted to rule out whiskers as well. .

I didn't get to work on the radio today and probably won't be able to
tomorrow either as work, (the kind you get paid for) has to take
precedence over my hobby. Although my "hobby" as of late has seemed to
be more like my nemesis to be exact. Thanks once again for all your
input. Lenny

 

[Franc Zabkar]

On Wed, 07 Mar 2012 20:35:40 -0800, Winston <Winston@Bigbrother.net>
put finger to keyboard and composed:

Did you happen to re-solder F IV pin 10 and
inspect the associated trace, Lenny?

I think Sylvia made a good point about it.

I agree. I'm convinced she's pinpointed the culprit.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[klem kedidelhopper]

On Mar 7, 11:35 pm, Winston <Wins...@Bigbrother.net> wrote:

klem kedidelhopper wrote:

(...)

I didn't get to work on the radio today and probably won't be able to
tomorrow either as work, (the kind you get paid for) has to take
precedence over my hobby. Although my "hobby" as of late has seemed to
be more like my nemesis to be exact. Thanks once again for all your
input. Lenny
T
Did you happen to re-solder F IV pin 10 and
inspect the associated trace, Lenny?

I think Sylvia made a good point about it.

It would be hugely amusing to measure the voltage dropped
across R21 and R28 during functional / non-functional
circumstances. You could use them as current sense resistors
to point you in the direction of the open or short.

--Winston

I know she was and it made perfect sense, but I was all over pin 10
and it's associated resistors. I had FIV out to replace AF126II in
fact and reinstalled it. I can't see anything wrong with the trace or
any traces for that matter. Tomorrow I'm going to take another look at
this. I'm going to check those two voltage drops, go and no go as you
suggested and I'll let you know. Lenny

 

[Winston]

klem kedidelhopper wrote:

On Mar 7, 11:35 pm, Winston<Wins...@Bigbrother.net> wrote:
klem kedidelhopper wrote:

(...)

I didn't get to work on the radio today and probably won't be able to
tomorrow either as work, (the kind you get paid for) has to take
precedence over my hobby. Although my "hobby" as of late has seemed to
be more like my nemesis to be exact. Thanks once again for all your
input. Lenny
T
Did you happen to re-solder F IV pin 10 and
inspect the associated trace, Lenny?

I think Sylvia made a good point about it.

It would be hugely amusing to measure the voltage dropped
across R21 and R28 during functional / non-functional
circumstances. You could use them as current sense resistors
to point you in the direction of the open or short.

--Winston

I know she was and it made perfect sense, but I was all over pin 10
and it's associated resistors. I had FIV out to replace AF126II in
fact and reinstalled it. I can't see anything wrong with the trace or
any traces for that matter. Tomorrow I'm going to take another look at
this. I'm going to check those two voltage drops, go and no go as you
suggested and I'll let you know. Lenny

Good.

I will Watch This Space.

--Winston

 

[spamtrap1888]

On Mar 6, 3:53 am, Sylvia Else <syl...@not.here.invalid> wrote:

On 5/03/2012 2:47 PM, klem kedidelhopper wrote:



I would like to ask for help once again with the repair of my own
personal old radio. I started this project almost a year ago, and it's
been on the back burner since then. But I had a little free time and
so I put it back on the bench. I would really like to see this radio
working again.

This is a Grundig "transistor 305", circa 1970 I think. The radio is
intermittent. I have been working on this set on and off for almost
the past year. I recently took some voltage measurements and there are
some serious differences in base  and emitter voltages in the last  IF
stage and the detector stage when this radio fails. I have tried many
things, heat and cold, including substituting all the transistors in
the RF and IF sections one at a time and have studied the schematic
until I felt a migraine coming on. l think that by now I could almost
draw it from memory, and I'm still coming up empty.

I considered trying to inject a signal and/or signal tracing, however
with the circuit voltages so far out of whack when it fails I think
that approach would be futile. The base and emitter voltages in these
three stages increase substantially when the radio quits. Some
voltages are jumping from for example 1.2V up to 4.0 V. With
conditions like this you would think that the cause would be obvious,
and perhaps I've been staring at this this too long and it is. However
the remedy has stubbornly eluded me thus far. The intermittent nature
of the problem is what makes it so difficult.

This is typical of what is going on: If the radio has been off for a
long period of time it will typically work for several hours and then
quit. In the beginning of this Quitting sequence, just after it first
quits it will try to come back on intermittently for a short period of
time, crackling etc, (as though something was intermittently breaking
down). Eventually it will just remain silent. There was an
electrolytic in the audio driver section, C57 a 100uf/3.0 volt with
slightly high ESR. Replacing it improved the low frequency audio
response, however the AF amplifier is not the problem though. You can
still get a good audio signal from the volume control out when it
fails. So the AF section seems to be unaffected. The voltages to that
part of the circuit substantiate that as well. And the RF and
oscillator circuit voltages during dead time seem to be fine as well.
The problem when it occurs affects both AM and FM.

The strange thing is that when powering this radio up again after a
shut down, the time it remains on before it quits once again is
directly proportional to the time that it has been off. For instance
if you leave it off overnight it might remain on for a half hour or so
the next morning before it quits again. Recently after trying it again
after months of it sitting idle it played for about 3 hours before it
quit. Then five minutes later when trying it again it quit almost
immediately. The few other electrolytics in the affected areas check
good on ESR and bridging them during dead time yielded no improvement
either. I have the schematic and I have uploaded it to the site listed
below.

I know that there are technicians out there better at this than I am,
and I would really appreciate it if someone could please take a  look
at the schematic along with the voltage readings I obtained during Go
and No Go conditions and give me your opinions. With three stages
affected I suspect that I'm looking for a common denominator but I'm
just not sure. The initial voltage readings (on turn on with the unit
working normally) will be listed in the left hand column. The voltage
readings during a failed condition are listed in the right hand
column.
The major differences are marked with an asterisk*.

I used to strap this radio to my bicycle when I was a kid and ride
around The Bronx with it. It has a great sound. I've owned it since I
was a teenager. I guess it's just a sentimental thing. Thanks for any
assistance. Lenny

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

                                      Voltage readingso
    Test point           Radio working:      Radio not working
  -------------------         --------------------
-------------------------
    E. AF178                -1.10V                    -1.20V
    B. AF178                -1.50V                    -1.50V
    E. AF124                -1.10V                    -1.20V
    B. AF124                -1.32V                    -1.44V
    E. AF121                -0.85V                    -0.90V
    B. AF121                -1.20V                    -1.30V
    E. AF126 (1)           -1.00V                    -3.70V *
    B. AF126 (1)           -1.20V                    -4.00V *
    E. AF126 (II)           -0.80V                    -3.70V *
    B. AF126 (II)           -1.10V                    -3.60V *
    E. AC151 (I)           - 0.90V                   -0.80V
    C. AC151 (I)           --3.05V                   -2.95V
    E. AC151 (II)          --0.66V                   -0.62V
    C. AC151 (II)          --3.20V                   -3.10V

Thanks once again for looking. Lenny

The bias of AF126 II is derived from the emitter of AF126 I (hereinafter
'the transistor'), so if the latter's bias arangements go awry, so will
the former's, which is thus of no interest.

If pin 10 of F IV became open circuit, the base of the transistor would
be pulled towards -9V through R5, R4, R26 and R21 in series, being a
total of 47.2K. For that to put the base at -4V requires a base current
of 0.1mA, there being no other source for the current.

For the emitter of the transistor to be at -3.7V requires a current of
4.5mA through R24 (the 820 ohm resistor). Given the calculated base
current, this would be the case if the beta of the transistor were 42,
which seems entirely plausible.

So if the transistor has a beta of around 40, the behaviour can be
explained by an intermittent open circuit at, or in the vicinity of, pin
10 of F IV.

Sylvia must mean R28 in series; R26 goes from the emitter of AF 126 I
to ground.

A reference I found says that the minimum hFE for the AF 126 is 50, so
a beta of 42 here is kind of sad.

http://alltransistors.com/transistor.php?transistor=21733

Now I'm wondering if the supply voltage is really 9V.

 

[amdx]

Today I took the time to thoroughly clean all the old caked on flux
off the areas that I've been working on and others also in order to
get a better look at the board. I removed R22 and it tested OK. I put
it back and reset the bias on the emitter of AF126 I to exactly 1.18V
With this bias all the other voltages seem to be very close to what's
shown on the schematic as well. I also did reflow some other suspect
solder connections using Kester mildly activated liquid flux. I
measured the following voltages before it became very intermittent
again. Group 1 is with the radio working.. Group 2 is after the radio
became very intermittent.
group1:
Vr28 .078V
vr21 .012V
Vr29 .0067V
Vr22 5.80V
Vr26 5.41V
Vr25 .057V

group 2
Vr28 2.00V
Vr21 2.10V
Vr29 .0011V
Vr22 2.30V
Vr26 2.60V
Vr25 .105V

I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit. I removed
the probe, it began working again briefly and then it started
crackling and soon after became constantly intermittent. Did I "shock"
something I wonder or was it just only a coincidence? Right now it's
in limbo between working and not, so intermittent that I can't really
look at anything.. Lenny

Have you tried heating the suspect transistors with the tip of your
soldering iron and dripping some freeze mist on them, and see what
changes. One at a time.
Also, you have several of the same model transistors in the circuit,
Swap them around!
Mikek

 

[klem kedidelhopper]

On Mar 8, 6:26 pm, Winston <Wins...@Bigbrother.net> wrote:

klem kedidelhopper wrote:
On Mar 7, 11:35 pm, Winston<Wins...@Bigbrother.net>  wrote:
klem kedidelhopper wrote:

(...)

I didn't get to work on the radio today and probably won't be able to
tomorrow either as work, (the kind you get paid for) has to take
precedence over my hobby. Although my "hobby" as of late has seemed to
be more like my nemesis to be exact. Thanks once again for all your
input. Lenny
T
Did you happen to re-solder F IV pin 10 and
inspect the associated trace, Lenny?

I think Sylvia made a good point about it.

It would be hugely amusing to measure the voltage dropped
across R21 and R28 during functional / non-functional
circumstances. You could use them as current sense resistors
to point you in the direction of the open or short.

--Winston

I know she was and it made perfect sense, but I was all over pin 10
and it's associated resistors. I had FIV out to replace AF126II in
fact and reinstalled it. I can't see anything wrong with the trace or
any traces for that matter. Tomorrow I'm going to take another look at
this. I'm going to check those two voltage drops, go and no go as you
suggested and I'll let you know. Lenny

Good.

I will Watch This Space.  

--Winston

Today I took the time to thoroughly clean all the old caked on flux
off the areas that I've been working on and others also in order to
get a better look at the board. I removed R22 and it tested OK. I put
it back and reset the bias on the emitter of AF126 I to exactly 1.18V
With this bias all the other voltages seem to be very close to what's
shown on the schematic as well. I also did reflow some other suspect
solder connections using Kester mildly activated liquid flux. I
measured the following voltages before it became very intermittent
again. Group 1 is with the radio working.. Group 2 is after the radio
became very intermittent.
group1:
Vr28 .078V
vr21 .012V
Vr29 .0067V
Vr22 5.80V
Vr26 5.41V
Vr25 .057V

group 2
Vr28 2.00V
Vr21 2.10V
Vr29 .0011V
Vr22 2.30V
Vr26 2.60V
Vr25 .105V

I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit. I removed
the probe, it began working again briefly and then it started
crackling and soon after became constantly intermittent. Did I "shock"
something I wonder or was it just only a coincidence? Right now it's
in limbo between working and not, so intermittent that I can't really
look at anything.. Lenny

 

[klem kedidelhopper]

On Mar 9, 4:45 pm, amdx <a...@knology.net> wrote:

Today I took the time to thoroughly clean all the old caked on flux
off the areas that I've been working on and others also in order to
get a better look at the board. I removed R22 and it tested OK. I put
it back and reset the bias on the emitter of AF126 I to exactly 1.18V
With this bias all the other voltages seem to be very close to what's
shown on the schematic as well.  I also did reflow some other suspect
solder connections using Kester mildly activated liquid flux. I
measured the following voltages before it became very intermittent
again. Group 1 is with the radio working.. Group 2 is after the radio
became very intermittent.
group1:
Vr28  .078V
vr21   .012V
Vr29  .0067V
Vr22  5.80V
Vr26  5.41V
Vr25  .057V

group 2
Vr28  2.00V
Vr21  2.10V
Vr29  .0011V
Vr22  2.30V
Vr26  2.60V
Vr25  .105V

I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit. I removed
the probe, it began working again briefly and then it started
crackling and soon after became constantly intermittent. Did I "shock"
something I wonder or was it just only a coincidence? Right now it's
in limbo between working and not, so intermittent that I can't really
look at anything.. Lenny

   Have you tried heating the suspect transistors with the tip of your
soldering iron and dripping some freeze mist on them, and see what
changes. One at a time.
  Also, you have several of the same model transistors in the circuit,
Swap them around!
                       Mikek

Well this may be a bit premature but in looking at the circuit I was
trying to determine what could possibly cause such a drastic change in
all these voltages, among the most drastic the voltage across R 22. So
on a whim I just replaced C38 and powered the radio up after a long
failure period. Normally under this condition it would quit almost
immediately. So far it has been working for about ten minutes. I hope
this doesn't end like my dream did the other morning....Lenny

 

[spamtrap1888]

On Mar 9, 2:18 pm, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

On Mar 9, 4:45 pm, amdx <a...@knology.net> wrote:



Today I took the time to thoroughly clean all the old caked on flux
off the areas that I've been working on and others also in order to
get a better look at the board. I removed R22 and it tested OK. I put
it back and reset the bias on the emitter of AF126 I to exactly 1.18V
With this bias all the other voltages seem to be very close to what's
shown on the schematic as well.  I also did reflow some other suspect
solder connections using Kester mildly activated liquid flux. I
measured the following voltages before it became very intermittent
again. Group 1 is with the radio working.. Group 2 is after the radio
became very intermittent.
group1:
Vr28  .078V
vr21   .012V
Vr29  .0067V
Vr22  5.80V
Vr26  5.41V
Vr25  .057V

group 2
Vr28  2.00V
Vr21  2.10V
Vr29  .0011V
Vr22  2.30V
Vr26  2.60V
Vr25  .105V

I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit. I removed
the probe, it began working again briefly and then it started
crackling and soon after became constantly intermittent. Did I "shock"
something I wonder or was it just only a coincidence? Right now it's
in limbo between working and not, so intermittent that I can't really
look at anything.. Lenny

   Have you tried heating the suspect transistors with the tip of your
soldering iron and dripping some freeze mist on them, and see what
changes. One at a time.
  Also, you have several of the same model transistors in the circuit,
Swap them around!
                       Mikek

Well this may be a bit premature but in looking at the circuit I was
trying to determine what could possibly cause such a drastic change in
all these voltages, among the most drastic the voltage across R 22. So
on a whim I just replaced C38 and powered the radio up after a long
failure period. Normally under this condition it would quit almost
immediately. So far it has been working for about ten minutes. I hope
this doesn't end like my dream did the other morning....Lenny

C38 was a foil cap, right? What kind did you replace it with?

 

[Winston]

klem kedidelhopper wrote:

On Mar 9, 4:45 pm, amdx<a...@knology.net> wrote:
Today I took the time to thoroughly clean all the old caked on flux
off the areas that I've been working on and others also in order to
get a better look at the board. I removed R22 and it tested OK. I put
it back and reset the bias on the emitter of AF126 I to exactly 1.18V
With this bias all the other voltages seem to be very close to what's
shown on the schematic as well. I also did reflow some other suspect
solder connections using Kester mildly activated liquid flux. I
measured the following voltages before it became very intermittent
again. Group 1 is with the radio working.. Group 2 is after the radio
became very intermittent.
group1:
Vr28 .078V
vr21 .012V
Vr29 .0067V
Vr22 5.80V
Vr26 5.41V
Vr25 .057V

group 2
Vr28 2.00V
Vr21 2.10V
Vr29 .0011V
Vr22 2.30V
Vr26 2.60V
Vr25 .105V

I don't know if this was a coincidence or what but I had taken the
above sets of voltages and had then decided to try to measure the E -
C voltage on AF126 I. As soon as I placed my probe on the collector I
must have detuned the circuit as the radio completely quit. I removed
the probe, it began working again briefly and then it started
crackling and soon after became constantly intermittent. Did I "shock"
something I wonder or was it just only a coincidence? Right now it's
in limbo between working and not, so intermittent that I can't really
look at anything.. Lenny

Have you tried heating the suspect transistors with the tip of your
soldering iron and dripping some freeze mist on them, and see what
changes. One at a time.
Also, you have several of the same model transistors in the circuit,
Swap them around!
Mikek

Well this may be a bit premature but in looking at the circuit I was
trying to determine what could possibly cause such a drastic change in
all these voltages, among the most drastic the voltage across R 22. So
on a whim I just replaced C38 and powered the radio up after a long
failure period. Normally under this condition it would quit almost
immediately. So far it has been working for about ten minutes. I hope
this doesn't end like my dream did the other morning....Lenny

It'd be great if C38 turned out to be our leaker, current-wise.

I'm still curious why the increased base current through
R21 (949 uA) is not completely apparent as an increased current in
the resistor that is in series with it, R28 (only 130 uA more,
not 949 uA more). Our increased current isn't going through R22
because during the failure, current through R22 *decreases*.



Resistance Eworking Iworking Enotworking Inotworking Edifference Idifference
R28 15000 0.07800000 0.00000520 2.00000000 0.00013333 1.92200000 0.00012813
R21 2200 0.01200000 0.00000545 2.10000000 0.00095455 2.08800000 0.00094909
R29 330 0.00670000 0.00002030 0.00110000 0.00000333 -0.00560000 -0.00001697
R22 15000 5.80000000 0.00038667 2.30000000 0.00015333 -3.50000000 -0.00023333
R26 180000 5.41000000 0.00003006 2.60000000 0.00001444 -2.81000000 -0.00001561
R25 10000 0.05700000 0.00000570 0.10500000 0.00001050 0.04800000 0.00000480
R24 820 1.00000000 0.00121951 3.70000000 0.00451220 2.70000000 0.00329268

--Winston

 

[Sylvia Else]

On 10/03/2012 7:08 AM, spamtrap1888 wrote:

On Mar 6, 3:53 am, Sylvia Else<syl...@not.here.invalid> wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:



I would like to ask for help once again with the repair of my own
personal old radio. I started this project almost a year ago, and it's
been on the back burner since then. But I had a little free time and
so I put it back on the bench. I would really like to see this radio
working again.

This is a Grundig "transistor 305", circa 1970 I think. The radio is
intermittent. I have been working on this set on and off for almost
the past year. I recently took some voltage measurements and there are
some serious differences in base and emitter voltages in the last IF
stage and the detector stage when this radio fails. I have tried many
things, heat and cold, including substituting all the transistors in
the RF and IF sections one at a time and have studied the schematic
until I felt a migraine coming on. l think that by now I could almost
draw it from memory, and I'm still coming up empty.

I considered trying to inject a signal and/or signal tracing, however
with the circuit voltages so far out of whack when it fails I think
that approach would be futile. The base and emitter voltages in these
three stages increase substantially when the radio quits. Some
voltages are jumping from for example 1.2V up to 4.0 V. With
conditions like this you would think that the cause would be obvious,
and perhaps I've been staring at this this too long and it is. However
the remedy has stubbornly eluded me thus far. The intermittent nature
of the problem is what makes it so difficult.

This is typical of what is going on: If the radio has been off for a
long period of time it will typically work for several hours and then
quit. In the beginning of this Quitting sequence, just after it first
quits it will try to come back on intermittently for a short period of
time, crackling etc, (as though something was intermittently breaking
down). Eventually it will just remain silent. There was an
electrolytic in the audio driver section, C57 a 100uf/3.0 volt with
slightly high ESR. Replacing it improved the low frequency audio
response, however the AF amplifier is not the problem though. You can
still get a good audio signal from the volume control out when it
fails. So the AF section seems to be unaffected. The voltages to that
part of the circuit substantiate that as well. And the RF and
oscillator circuit voltages during dead time seem to be fine as well.
The problem when it occurs affects both AM and FM.

The strange thing is that when powering this radio up again after a
shut down, the time it remains on before it quits once again is
directly proportional to the time that it has been off. For instance
if you leave it off overnight it might remain on for a half hour or so
the next morning before it quits again. Recently after trying it again
after months of it sitting idle it played for about 3 hours before it
quit. Then five minutes later when trying it again it quit almost
immediately. The few other electrolytics in the affected areas check
good on ESR and bridging them during dead time yielded no improvement
either. I have the schematic and I have uploaded it to the site listed
below.

I know that there are technicians out there better at this than I am,
and I would really appreciate it if someone could please take a look
at the schematic along with the voltage readings I obtained during Go
and No Go conditions and give me your opinions. With three stages
affected I suspect that I'm looking for a common denominator but I'm
just not sure. The initial voltage readings (on turn on with the unit
working normally) will be listed in the left hand column. The voltage
readings during a failed condition are listed in the right hand
column.
The major differences are marked with an asterisk*.

I used to strap this radio to my bicycle when I was a kid and ride
around The Bronx with it. It has a great sound. I've owned it since I
was a teenager. I guess it's just a sentimental thing. Thanks for any
assistance. Lenny

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

Voltage readingso
Test point Radio working: Radio not working
------------------- --------------------
-------------------------
E. AF178 -1.10V -1.20V
B. AF178 -1.50V -1.50V
E. AF124 -1.10V -1.20V
B. AF124 -1.32V -1.44V
E. AF121 -0.85V -0.90V
B. AF121 -1.20V -1.30V
E. AF126 (1) -1.00V -3.70V *
B. AF126 (1) -1.20V -4.00V *
E. AF126 (II) -0.80V -3.70V *
B. AF126 (II) -1.10V -3.60V *
E. AC151 (I) - 0.90V -0.80V
C. AC151 (I) --3.05V -2.95V
E. AC151 (II) --0.66V -0.62V
C. AC151 (II) --3.20V -3.10V

Thanks once again for looking. Lenny

The bias of AF126 II is derived from the emitter of AF126 I (hereinafter
'the transistor'), so if the latter's bias arangements go awry, so will
the former's, which is thus of no interest.

If pin 10 of F IV became open circuit, the base of the transistor would
be pulled towards -9V through R5, R4, R26 and R21 in series, being a
total of 47.2K. For that to put the base at -4V requires a base current
of 0.1mA, there being no other source for the current.

For the emitter of the transistor to be at -3.7V requires a current of
4.5mA through R24 (the 820 ohm resistor). Given the calculated base
current, this would be the case if the beta of the transistor were 42,
which seems entirely plausible.

So if the transistor has a beta of around 40, the behaviour can be
explained by an intermittent open circuit at, or in the vicinity of, pin
10 of F IV.


Sylvia must mean R28 in series; R26 goes from the emitter of AF 126 I
to ground.

A reference I found says that the minimum hFE for the AF 126 is 50, so
a beta of 42 here is kind of sad.

http://alltransistors.com/transistor.php?transistor=21733

Now I'm wondering if the supply voltage is really 9V.

You're right about the supply voltage. I just looked at the battery, but
in fact the radio takes its current from the battery through a resistor,
and the markings on the circuit indicate that this reduces the supply to
7.5V. Applying the correction gives a beta of 50.4, which is admittedly
still right at the low end of the spec you've found.

Offsetting that, the base is also being pulled down through R22, whose
actual value we don't know. I assumed it would be closer to 1M, on the
grounds that otherwise a smaller valued trimmer would have been used.

It's a bit moot, anyway, since the OP says that he's already resoldered
pin 10 of IF IV.

My next step would be to look at the voltage on what I think is pin 8 of
IF IV (i.e., the pin connected to R31 and R28.


Sylvia.

 

[klem kedidelhopper]

On Mar 9, 10:58 pm, Sylvia Else <syl...@not.here.invalid> wrote:

On 10/03/2012 7:08 AM, spamtrap1888 wrote:









On Mar 6, 3:53 am, Sylvia Else<syl...@not.here.invalid>  wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

I would like to ask for help once again with the repair of my own
personal old radio. I started this project almost a year ago, and it's
been on the back burner since then. But I had a little free time and
so I put it back on the bench. I would really like to see this radio
working again.

This is a Grundig "transistor 305", circa 1970 I think. The radio is
intermittent. I have been working on this set on and off for almost
the past year. I recently took some voltage measurements and there are
some serious differences in base  and emitter voltages in the last  IF
stage and the detector stage when this radio fails. I have tried many
things, heat and cold, including substituting all the transistors in
the RF and IF sections one at a time and have studied the schematic
until I felt a migraine coming on. l think that by now I could almost
draw it from memory, and I'm still coming up empty.

I considered trying to inject a signal and/or signal tracing, however
with the circuit voltages so far out of whack when it fails I think
that approach would be futile. The base and emitter voltages in these
three stages increase substantially when the radio quits. Some
voltages are jumping from for example 1.2V up to 4.0 V. With
conditions like this you would think that the cause would be obvious,
and perhaps I've been staring at this this too long and it is. However
the remedy has stubbornly eluded me thus far. The intermittent nature
of the problem is what makes it so difficult.

This is typical of what is going on: If the radio has been off for a
long period of time it will typically work for several hours and then
quit. In the beginning of this Quitting sequence, just after it first
quits it will try to come back on intermittently for a short period of
time, crackling etc, (as though something was intermittently breaking
down). Eventually it will just remain silent. There was an
electrolytic in the audio driver section, C57 a 100uf/3.0 volt with
slightly high ESR. Replacing it improved the low frequency audio
response, however the AF amplifier is not the problem though. You can
still get a good audio signal from the volume control out when it
fails. So the AF section seems to be unaffected. The voltages to that
part of the circuit substantiate that as well. And the RF and
oscillator circuit voltages during dead time seem to be fine as well.
The problem when it occurs affects both AM and FM.

The strange thing is that when powering this radio up again after a
shut down, the time it remains on before it quits once again is
directly proportional to the time that it has been off. For instance
if you leave it off overnight it might remain on for a half hour or so
the next morning before it quits again. Recently after trying it again
after months of it sitting idle it played for about 3 hours before it
quit. Then five minutes later when trying it again it quit almost
immediately. The few other electrolytics in the affected areas check
good on ESR and bridging them during dead time yielded no improvement
either. I have the schematic and I have uploaded it to the site listed
below.

I know that there are technicians out there better at this than I am,
and I would really appreciate it if someone could please take a  look
at the schematic along with the voltage readings I obtained during Go
and No Go conditions and give me your opinions. With three stages
affected I suspect that I'm looking for a common denominator but I'm
just not sure. The initial voltage readings (on turn on with the unit
working normally) will be listed in the left hand column. The voltage
readings during a failed condition are listed in the right hand
column.
The major differences are marked with an asterisk*.

I used to strap this radio to my bicycle when I was a kid and ride
around The Bronx with it. It has a great sound. I've owned it since I
was a teenager. I guess it's just a sentimental thing. Thanks for any
assistance. Lenny

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

                                       Voltage readingso
     Test point           Radio working:      Radio not working
   -------------------         --------------------
-------------------------
     E. AF178                -1.10V                    -1.20V
     B. AF178                -1.50V                    -1.50V
     E. AF124                -1.10V                    -1.20V
     B. AF124                -1.32V                    -1.44V
     E. AF121                -0.85V                    -0.90V
     B. AF121                -1.20V                    -1.30V
     E. AF126 (1)           -1.00V                    -3.70V *
     B. AF126 (1)           -1.20V                    -4.00V *
     E. AF126 (II)           -0.80V                    -3.70V *
     B. AF126 (II)           -1.10V                    -3.60V *
     E. AC151 (I)           - 0.90V                   -0.80V
     C. AC151 (I)           --3.05V                   -2.95V
     E. AC151 (II)          --0.66V                   -0.62V
     C. AC151 (II)          --3.20V                   -3.10V

Thanks once again for looking. Lenny

The bias of AF126 II is derived from the emitter of AF126 I (hereinafter
'the transistor'), so if the latter's bias arangements go awry, so will
the former's, which is thus of no interest.

If pin 10 of F IV became open circuit, the base of the transistor would
be pulled towards -9V through R5, R4, R26 and R21 in series, being a
total of 47.2K. For that to put the base at -4V requires a base current
of 0.1mA, there being no other source for the current.

For the emitter of the transistor to be at -3.7V requires a current of
4.5mA through R24 (the 820 ohm resistor). Given the calculated base
current, this would be the case if the beta of the transistor were 42,
which seems entirely plausible.

So if the transistor has a beta of around 40, the behaviour can be
explained by an intermittent open circuit at, or in the vicinity of, pin
10 of F IV.

Sylvia must mean R28 in series; R26 goes from the emitter of AF 126 I
to ground.

A reference I found says that the minimum hFE for the AF 126 is 50, so
a beta of 42 here is kind of sad.

http://alltransistors.com/transistor.php?transistor=21733

Now I'm wondering if the supply voltage is really 9V.

You're right about the supply voltage. I just looked at the battery, but
in fact the radio takes its current from the battery through a resistor,
and the markings on the circuit indicate that this reduces the supply to
7.5V. Applying the correction gives a beta of 50.4, which is admittedly
still right at the low end of the spec you've found.

Offsetting that, the base is also being pulled down through R22, whose
actual value we don't know. I assumed it would be closer to 1M, on the
grounds that otherwise a smaller valued trimmer would have been used.

It's a bit moot, anyway, since the OP says that he's already resoldered
pin 10 of IF IV.

My next step would be to look at the voltage on what I think is pin 8 of
IF IV (i.e., the pin connected to R31 and R28.

Sylvia.

I used an epoxe cap.. The original was tubular and assuming foil with
a polarity stripe. It doesn't seem to matter though. I found R22 set
to about center when I pulled it. It measured about even on both sides
of the wiper. I probably turned it about 90 degrees after my first
adjustment for Vr24.(before replacing C38). But now I'm not so sure
that that all my readings are correct. If you look at the note on the
schematic it reads: "voltages measured with Grundig VTVM at battery
voltage 7.50V, "etc". This seems to suggest, and it was the
impression that I got that for whatever reason I was supposed to lower
the applied voltage to 7.50 V as measured at the battery terminals to
make my voltage measurements. Sylvia pointed out that (with the
positive ground arrangement) the applied voltage (negative) goes
through the 100 ohm resistor R46 to what we would consider as
"ground", the positive rail. This reverse polarity takes a bit of
getting used to...

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A. So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny

 

[klem kedidelhopper]

On Mar 10, 11:05 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

On Mar 9, 10:58 pm, Sylvia Else <syl...@not.here.invalid> wrote:









On 10/03/2012 7:08 AM, spamtrap1888 wrote:

On Mar 6, 3:53 am, Sylvia Else<syl...@not.here.invalid>  wrote:
On 5/03/2012 2:47 PM, klem kedidelhopper wrote:

I would like to ask for help once again with the repair of my own
personal old radio. I started this project almost a year ago, and it's
been on the back burner since then. But I had a little free time and
so I put it back on the bench. I would really like to see this radio
working again.

This is a Grundig "transistor 305", circa 1970 I think. The radio is
intermittent. I have been working on this set on and off for almost
the past year. I recently took some voltage measurements and there are
some serious differences in base  and emitter voltages in the last  IF
stage and the detector stage when this radio fails. I have tried many
things, heat and cold, including substituting all the transistors in
the RF and IF sections one at a time and have studied the schematic
until I felt a migraine coming on. l think that by now I could almost
draw it from memory, and I'm still coming up empty.

I considered trying to inject a signal and/or signal tracing, however
with the circuit voltages so far out of whack when it fails I think
that approach would be futile. The base and emitter voltages in these
three stages increase substantially when the radio quits. Some
voltages are jumping from for example 1.2V up to 4.0 V. With
conditions like this you would think that the cause would be obvious,
and perhaps I've been staring at this this too long and it is. However
the remedy has stubbornly eluded me thus far. The intermittent nature
of the problem is what makes it so difficult.

This is typical of what is going on: If the radio has been off for a
long period of time it will typically work for several hours and then
quit. In the beginning of this Quitting sequence, just after it first
quits it will try to come back on intermittently for a short period of
time, crackling etc, (as though something was intermittently breaking
down). Eventually it will just remain silent. There was an
electrolytic in the audio driver section, C57 a 100uf/3.0 volt with
slightly high ESR. Replacing it improved the low frequency audio
response, however the AF amplifier is not the problem though. You can
still get a good audio signal from the volume control out when it
fails. So the AF section seems to be unaffected. The voltages to that
part of the circuit substantiate that as well. And the RF and
oscillator circuit voltages during dead time seem to be fine as well.
The problem when it occurs affects both AM and FM.

The strange thing is that when powering this radio up again after a
shut down, the time it remains on before it quits once again is
directly proportional to the time that it has been off. For instance
if you leave it off overnight it might remain on for a half hour or so
the next morning before it quits again. Recently after trying it again
after months of it sitting idle it played for about 3 hours before it
quit. Then five minutes later when trying it again it quit almost
immediately. The few other electrolytics in the affected areas check
good on ESR and bridging them during dead time yielded no improvement
either. I have the schematic and I have uploaded it to the site listed
below.

I know that there are technicians out there better at this than I am,
and I would really appreciate it if someone could please take a  look
at the schematic along with the voltage readings I obtained during Go
and No Go conditions and give me your opinions. With three stages
affected I suspect that I'm looking for a common denominator but I'm
just not sure. The initial voltage readings (on turn on with the unit
working normally) will be listed in the left hand column. The voltage
readings during a failed condition are listed in the right hand
column.
The major differences are marked with an asterisk*.

I used to strap this radio to my bicycle when I was a kid and ride
around The Bronx with it. It has a great sound. I've owned it since I
was a teenager. I guess it's just a sentimental thing. Thanks for any
assistance. Lenny

http://dl.dropbox.com/u/65394789/Grundig%20large%20schematic.pdf

                                       Voltage readingso
     Test point           Radio working:      Radio not working
   -------------------         --------------------
-------------------------
     E. AF178                -1.10V                    -1.20V
     B. AF178                -1.50V                    -1.50V
     E. AF124                -1.10V                    -1.20V
     B. AF124                -1.32V                    -1.44V
     E. AF121                -0.85V                    -0.90V
     B. AF121                -1.20V                    -1.30V
     E. AF126 (1)           -1.00V                    -3.70V *
     B. AF126 (1)           -1.20V                    -4.00V *
     E. AF126 (II)           -0.80V                    -3.70V *
     B. AF126 (II)           -1.10V                    -3.60V *
     E. AC151 (I)           - 0.90V                   -0.80V
     C. AC151 (I)           --3.05V                   -2.95V
     E. AC151 (II)          --0.66V                   -0.62V
     C. AC151 (II)          --3.20V                   -3.10V

Thanks once again for looking. Lenny

The bias of AF126 II is derived from the emitter of AF126 I (hereinafter
'the transistor'), so if the latter's bias arangements go awry, so will
the former's, which is thus of no interest.

If pin 10 of F IV became open circuit, the base of the transistor would
be pulled towards -9V through R5, R4, R26 and R21 in series, being a
total of 47.2K. For that to put the base at -4V requires a base current
of 0.1mA, there being no other source for the current.

For the emitter of the transistor to be at -3.7V requires a current of
4.5mA through R24 (the 820 ohm resistor). Given the calculated base
current, this would be the case if the beta of the transistor were 42,
which seems entirely plausible.

So if the transistor has a beta of around 40, the behaviour can be
explained by an intermittent open circuit at, or in the vicinity of, pin
10 of F IV.

Sylvia must mean R28 in series; R26 goes from the emitter of AF 126 I
to ground.

A reference I found says that the minimum hFE for the AF 126 is 50, so
a beta of 42 here is kind of sad.

http://alltransistors.com/transistor.php?transistor=21733

Now I'm wondering if the supply voltage is really 9V.

You're right about the supply voltage. I just looked at the battery, but
in fact the radio takes its current from the battery through a resistor,
and the markings on the circuit indicate that this reduces the supply to
7.5V. Applying the correction gives a beta of 50.4, which is admittedly
still right at the low end of the spec you've found.

Offsetting that, the base is also being pulled down through R22, whose
actual value we don't know. I assumed it would be closer to 1M, on the
grounds that otherwise a smaller valued trimmer would have been used.

It's a bit moot, anyway, since the OP says that he's already resoldered
pin 10 of IF IV.

My next step would be to look at the voltage on what I think is pin 8 of
IF IV (i.e., the pin connected to R31 and R28.

Sylvia.

I used an epoxe cap.. The original was tubular and assuming foil with
a polarity stripe. It doesn't seem to matter though. I found R22 set
to about center when I pulled it. It measured about even on both sides
of the wiper. I probably turned it about 90 degrees after my first
adjustment for Vr24.(before replacing C38). But now I'm not so sure
that that all my readings are correct. If you look at the note on the
schematic it reads: "voltages measured with Grundig VTVM at battery
voltage 7.50V, "etc".  This seems to suggest, and it was the
impression that I got that for whatever reason I was supposed to lower
the applied voltage to 7.50 V as measured at the battery terminals to
make my voltage measurements. Sylvia pointed out that (with the
positive ground arrangement) the applied voltage (negative) goes
through the 100 ohm resistor R46 to what we would consider as
"ground", the positive rail. This reverse polarity takes a bit of
getting used to...

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However  I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A.  So now I'm really confused. Are you supposed
...

read more ť

I used an epoxe cap.. The original was tubular and assuming foil with
a polarity stripe. It doesn't seem to matter though. I found R22 set
to about center when I pulled it. It measured about even on both sides
of the wiper. I probably turned it about 90 degrees after my first
adjustment for Vr24.(before replacing C38). But now I'm not so sure
that that all my readings are correct. If you look at the note on the
schematic it reads: "voltages measured with Grundig VTVM at battery
voltage 7.50V, "etc". This seems to suggest, and it was the
impression that I got that for whatever reason I was supposed to lower
the applied voltage to 7.50 V as measured at the battery terminals to
make my voltage measurements. Sylvia pointed out that (with the
positive ground arrangement) the applied voltage (negative) goes
through the 100 ohm resistor R46 to what we would consider as
"ground", the positive rail. This reverse polarity takes a bit of
getting used to...

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A. So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny

 

[Winston]

klem kedidelhopper wrote:

(...)

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A. So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny

'Sounds like your 'rail voltage' ended up at 6.66 V considering
the 0.84 V drop in R46 or about 90 mV below the minimum indicated
on the schematic.

Were it me, I'd adjust the power supply until the rail voltage
measured, say 6.88 V.

It's an exercise anyway because you apparently found
and fixed the bug.

That's the important thing.

--Winston

 

[Sylvia Else]

On 11/03/2012 3:08 AM, klem kedidelhopper wrote:

So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny

The situation mostly doesn't arise. With a few (possibly only one)
exceptions, the annotated voltages are between two specified points, not
a voltage relative to ground. Indeed, most are between two points
neither of which is anywhere near ground.

The base and emitter voltages are relative to the positive supply rail.
Given the way that the biases are obtained, they wouldn't have been
sensitive to the supply voltage, which is no doubt intentional given
that the supply voltage from a battery will change as the battery is
consumed.

On another note, while replacing C38 has apparently cured the problem,
I'm totally mystified as to why. It would imply that C38 had failed such
that it intermittently behaved as if it had a resistance of many
kilo-ohms in parallel with it. It seems an unlikely failure mode for a
capacitor.

Sylvia.

 

[klem kedidelhopper]

On Mar 10, 7:08 pm, Winston <Wins...@Bigbrother.net> wrote:

klem kedidelhopper wrote:

(...)

There is a note near the battery connector which indicates what
appears to be a quiescent current between .020 and .022A. In fact when
I started this project I measured .025A on the bench power supply with
7.50V applied to the battery terminals. Therefore, given my initial
quiescent current reading, if all that current is indeed flowing
through R46 then I should have dropped 2.50V across R46. However  I
never monitored that point so I didn't know. This morning the radio
was still working and I noted that Vr46 was .840V. Quiescent current
is still .025A.  So now I'm really confused. Are you supposed to start
off with 9.0 Volts at the battery terminals for voltage measurement
purposes or is it 7.50 Volts? I can say with every certainty that with
7.50V applied the actual circuit voltages did almost mimic what the
schematic shows when the radio was operational. Or has my supply been
at least 1.50V - 2.50V too low throughout this experiment? Lenny

'Sounds like your 'rail voltage' ended up at 6.66 V considering
the 0.84 V drop in R46 or about 90 mV below the minimum indicated
on the schematic.

Were it me, I'd adjust the power supply until the rail voltage
measured, say 6.88 V.

It's an exercise anyway because you apparently found
and fixed the bug.

That's the important thing.  

--Winston

Well I still have my fingers crossed but it does look hopeful. Lenny