Grundig AM/FM portable "Transistor 305" troubleshooting

[Winston]

Sylvia Else wrote:

(...)

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.

C38 could be a total red herring.

Lenny said yesterday afternoon:

"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."

It may just be that the base of AF 126 I is shorting out against
its grounded can, causing it to saturate intermittently.
If C38 is close to AF126 I, Lenny might have 'bumped' the short
open whilst replacing C38.

--Winston

 

[Sylvia Else]

On 11/03/2012 4:38 PM, Winston wrote:

Sylvia Else wrote:

(...)

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.

C38 could be a total red herring.

Lenny said yesterday afternoon:

"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."

It may just be that the base of AF 126 I is shorting out against
its grounded can, causing it to saturate intermittently.
If C38 is close to AF126 I, Lenny might have 'bumped' the short
open whilst replacing C38.

--Winston

If the base were shorted to the grounded can, then the base voltage
would be at ground level, but it's not. That's the puzzle with this
fault - finding a credible intermitten failure that will put the base at
the voltage level seen.

Sylvia.

 

[Sylvia Else]

On 6/03/2012 10:53 PM, Sylvia Else wrote:

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.

Belatedly, I realise that this cannot be correct. If pin 10 of F IV were
to become open circuit, there would be no sink for the current through
the diode 1.4 St1, and the bases of AF178 and AF124, and the latter
would rise to the positive rail.

I'm left wondering about the voltage on the collector of AF121. If it
turned out to be -4V (which seems a plausible enough operating point),
then there could be an intermittent short across the windings of FII,
thereby connecting the base of AF126 I more or less directly to the
collector of AF121.

Sylvia.

 

[klem kedidelhopper]

On Mar 11, 7:39 am, Sylvia Else <syl...@not.here.invalid> wrote:

On 6/03/2012 10:53 PM, Sylvia Else wrote:

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.

Belatedly, I realise that this cannot be correct. If pin 10 of F IV were
to become open circuit, there would be no sink for the current through
the diode 1.4 St1, and the bases of AF178 and AF124, and the latter
would rise to the positive rail.

I'm left wondering about the voltage on the collector of AF121. If it
turned out to be -4V (which seems a plausible enough operating point),
then there could be an intermittent short across the windings of FII,
thereby connecting the base of AF126 I more or less directly to the
collector of AF121.

Sylvia.

Given the intermittent nature of this job so far I have trouble
actually saying that it's repaired, However I now have two periods of
time wherein it has operated without a problem for at least 14 hours
continuously, with a few hours powered down in between. It's never
done that since this problem began. So I am starting to feel a bit
more certain about the validity of this repair.

I reset the bias to 1.18V yesterday and last night I noted that it had
drifted up to 1.23V. It's not a big excursion but I will keep an eye
on it though comparing initial turn on with after a few hours running
over the next couple of days or so.

There are a few things I still have to do. All the can grounds
are.currently unsoldered and disconnected from the circuit.
After I log some more time on this radio I'll need to restore those
and see if that makes any difference. I don't expect that it will but
I want to take this one step at a time.

The other thing I want to do is remove FIV one more time and put back
the transistor, (AF126 II) that was originally there. In actuality
that transistor is an AF124 which I purchased from Grundig service in
Manhattan about 35 years ago. The AF126 II was the problem with the
radio when I got it from a friend back around 1975 and not having a
126, Grundig substituted the 124 for me. It never seemed to affect the
alignment so I see no reason to not use it over again. The replacement
transistors that I have been using through out this repair came from a
friend in Sweden and are likely as old as my originals anyway.

So as it turns out I didn't need to replace any of them. Therefore the
alignment shouldn't have been affected, nor should the replacement of
C38 have affected the alignment much if at all either.

It occurred to me that if this were a customers radio, I'd likely own
their home at this point...

Lenny

 

[Winston]

Sylvia Else wrote:

On 11/03/2012 4:38 PM, Winston wrote:
Sylvia Else wrote:

(...)

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.

C38 could be a total red herring.

Lenny said yesterday afternoon:

"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."

It may just be that the base of AF 126 I is shorting out against
its grounded can, causing it to saturate intermittently.
If C38 is close to AF126 I, Lenny might have 'bumped' the short
open whilst replacing C38.

--Winston

If the base were shorted to the grounded can, then the base voltage would be at ground level, but it's not. That's the
puzzle with this fault - finding a credible intermitten failure that will put the base at the voltage level seen.

Yup. You're right.

It almost must have been be an intermittently leaky C38.

--Winston

 

[Winston]

klem kedidelhopper wrote:

On Mar 11, 7:39 am, Sylvia Else<syl...@not.here.invalid> wrote:
On 6/03/2012 10:53 PM, Sylvia Else wrote:

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.

Belatedly, I realise that this cannot be correct. If pin 10 of F IV were
to become open circuit, there would be no sink for the current through
the diode 1.4 St1, and the bases of AF178 and AF124, and the latter
would rise to the positive rail.

I'm left wondering about the voltage on the collector of AF121. If it
turned out to be -4V (which seems a plausible enough operating point),
then there could be an intermittent short across the windings of FII,
thereby connecting the base of AF126 I more or less directly to the
collector of AF121.

Sylvia.


Given the intermittent nature of this job so far I have trouble
actually saying that it's repaired, However I now have two periods of
time wherein it has operated without a problem for at least 14 hours
continuously, with a few hours powered down in between. It's never
done that since this problem began. So I am starting to feel a bit
more certain about the validity of this repair.

I reset the bias to 1.18V yesterday and last night I noted that it had
drifted up to 1.23V. It's not a big excursion but I will keep an eye
on it though comparing initial turn on with after a few hours running
over the next couple of days or so.

There are a few things I still have to do. All the can grounds
are.currently unsoldered and disconnected from the circuit.
After I log some more time on this radio I'll need to restore those
and see if that makes any difference. I don't expect that it will but
I want to take this one step at a time.

The other thing I want to do is remove FIV one more time and put back
the transistor, (AF126 II) that was originally there. In actuality
that transistor is an AF124 which I purchased from Grundig service in
Manhattan about 35 years ago. The AF126 II was the problem with the
radio when I got it from a friend back around 1975 and not having a
126, Grundig substituted the 124 for me. It never seemed to affect the
alignment so I see no reason to not use it over again. The replacement
transistors that I have been using through out this repair came from a
friend in Sweden and are likely as old as my originals anyway.

So as it turns out I didn't need to replace any of them. Therefore the
alignment shouldn't have been affected, nor should the replacement of
C38 have affected the alignment much if at all either.

Were it me, I would move on to other things.

If the radio repeats the symptoms, then it wasn't an
intermittently leaky C38. At that point, I would
open the investigation once more.

Hey, it's working. Be happy.

It occurred to me that if this were a customers radio, I'd likely own
their home at this point...

More likely, they'd own your shop.

--Winston

 

[klem kedidelhopper]

On Mar 11, 3:56 pm, Winston <Wins...@Bigbrother.net> wrote:

klem kedidelhopper wrote:
On Mar 11, 7:39 am, Sylvia Else<syl...@not.here.invalid>  wrote:
On 6/03/2012 10:53 PM, Sylvia Else wrote:

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.

Belatedly, I realise that this cannot be correct. If pin 10 of F IV were
to become open circuit, there would be no sink for the current through
the diode 1.4 St1, and the bases of AF178 and AF124, and the latter
would rise to the positive rail.

I'm left wondering about the voltage on the collector of AF121. If it
turned out to be -4V (which seems a plausible enough operating point),
then there could be an intermittent short across the windings of FII,
thereby connecting the base of AF126 I more or less directly to the
collector of AF121.

Sylvia.

Given the intermittent nature of this job so far I have trouble
actually saying that it's repaired, However I now have two periods of
time wherein it has operated without a problem for at least 14 hours
continuously, with a few hours powered down in between. It's never
done that since this problem began. So I am starting to feel a bit
more certain about the validity of this repair.

I reset the bias to 1.18V yesterday and last night I noted that it had
drifted up to 1.23V. It's not a big excursion but I will keep an eye
on it though comparing initial turn on with after a few hours running
over the next couple of days or so.

There are a few things I still have to do. All the can grounds
are.currently unsoldered and disconnected from the circuit.
After I log some more time on this radio I'll need to restore those
and see if that makes any difference. I don't expect that it will but
I want to take this one step at a time.

The other thing I want to do is remove FIV one more time and put back
the transistor, (AF126 II) that was originally there. In actuality
that transistor is an AF124 which I purchased from Grundig service in
Manhattan about 35 years ago. The AF126 II was the problem with the
radio when I got it from a friend back around 1975 and not having a
126, Grundig substituted the 124 for me. It never seemed to affect the
alignment so I see no reason to not use it over again. The replacement
transistors that I have been using through out this repair came from a
friend in Sweden and are likely as old as my originals anyway.

So as it turns out I didn't need to replace any of them. Therefore the
alignment shouldn't have been affected, nor should the replacement of
C38 have affected the alignment much if at all either.

Were it me, I would move on to other things.

If the radio repeats the symptoms, then it wasn't an
intermittently leaky C38.  At that point, I would
open the investigation once more.

Hey, it's working.  Be happy.  



It occurred to me that if this were a customers radio, I'd likely own
their home at this point...

More likely, they'd own your shop.  

--Winston

So I've replaced all the original transistors, resoldered the
transistor cans, (grounds) and reset the bias with R22 to -1.18V with
7.50V applied to the battery connector. That bias voltage however
rises to -1.33V when the supply is boosted up to 9.0V. So as I
expected, it seems that the supply voltage does make a small
difference in bias. Does anyone else have any theories as to what
Grundig may have had in mind when they specified that bias as well as
the other circuit voltages? Was it with 7.50V applied or 9.0V? Lenny

 

[Winston]

klem kedidelhopper wrote:

On Mar 11, 3:56 pm, Winston<Wins...@Bigbrother.net> wrote:

(...)

Were it me, I would move on to other things.

If the radio repeats the symptoms, then it wasn't an
intermittently leaky C38. At that point, I would
open the investigation once more.

Hey, it's working. Be happy.

(...)

So I've replaced all the original transistors, resoldered the
transistor cans, (grounds) and reset the bias with R22 to -1.18V with
7.50V applied to the battery connector. That bias voltage however
rises to -1.33V when the supply is boosted up to 9.0V. So as I
expected, it seems that the supply voltage does make a small
difference in bias. Does anyone else have any theories as to what
Grundig may have had in mind when they specified that bias as well as
the other circuit voltages? Was it with 7.50V applied or 9.0V? Lenny

The way I read Grundig's schematic notes, they want us to set the
lab supply so that 7.0 V is seen on the power rail if in 'Medium Wave'
mode or 6.75 V on the rail if in 'FM' mode.

If that requires 7.8 V on the actual battery connector or 12.7 V
on the actual battery connector, it does not matter as long as the
rail voltage is set correctly for the function chosen.

They want the radio to function well with brand new batteries or
almost dead batteries.

I would not sweat over bias drift when a real battery is connected.
The documentation is pretty clear on their requirement.

--Winston

 

[josephkk]

On Sat, 10 Mar 2012 08:08:12 -0800 (PST), klem kedidelhopper
<captainvideo462009@gmail.com> wrote:

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

After reading this thread through to this post i have a question. Can you
find the traces where R24 and R27 meet? I suspect a crack between there
and the + rail.

?-)

 

[Sylvia Else]

On 12/03/2012 3:20 PM, josephkk wrote:

On Sat, 10 Mar 2012 08:08:12 -0800 (PST), klem kedidelhopper
captainvideo462009@gmail.com> wrote:

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

After reading this thread through to this post i have a question. Can you
find the traces where R24 and R27 meet? I suspect a crack between there
and the + rail.

?-)

That wouldn't have the observed effect on the base and emitter voltages.

Sylvia.

 

[Sylvia Else]

On 12/03/2012 12:05 PM, klem kedidelhopper wrote:

On Mar 11, 3:56 pm, Winston<Wins...@Bigbrother.net> wrote:
klem kedidelhopper wrote:
On Mar 11, 7:39 am, Sylvia Else<syl...@not.here.invalid> wrote:
On 6/03/2012 10:53 PM, Sylvia Else wrote:

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.

Belatedly, I realise that this cannot be correct. If pin 10 of F IV were
to become open circuit, there would be no sink for the current through
the diode 1.4 St1, and the bases of AF178 and AF124, and the latter
would rise to the positive rail.

I'm left wondering about the voltage on the collector of AF121. If it
turned out to be -4V (which seems a plausible enough operating point),
then there could be an intermittent short across the windings of FII,
thereby connecting the base of AF126 I more or less directly to the
collector of AF121.

Sylvia.

Given the intermittent nature of this job so far I have trouble
actually saying that it's repaired, However I now have two periods of
time wherein it has operated without a problem for at least 14 hours
continuously, with a few hours powered down in between. It's never
done that since this problem began. So I am starting to feel a bit
more certain about the validity of this repair.

I reset the bias to 1.18V yesterday and last night I noted that it had
drifted up to 1.23V. It's not a big excursion but I will keep an eye
on it though comparing initial turn on with after a few hours running
over the next couple of days or so.

There are a few things I still have to do. All the can grounds
are.currently unsoldered and disconnected from the circuit.
After I log some more time on this radio I'll need to restore those
and see if that makes any difference. I don't expect that it will but
I want to take this one step at a time.

The other thing I want to do is remove FIV one more time and put back
the transistor, (AF126 II) that was originally there. In actuality
that transistor is an AF124 which I purchased from Grundig service in
Manhattan about 35 years ago. The AF126 II was the problem with the
radio when I got it from a friend back around 1975 and not having a
126, Grundig substituted the 124 for me. It never seemed to affect the
alignment so I see no reason to not use it over again. The replacement
transistors that I have been using through out this repair came from a
friend in Sweden and are likely as old as my originals anyway.

So as it turns out I didn't need to replace any of them. Therefore the
alignment shouldn't have been affected, nor should the replacement of
C38 have affected the alignment much if at all either.

Were it me, I would move on to other things.

If the radio repeats the symptoms, then it wasn't an
intermittently leaky C38. At that point, I would
open the investigation once more.

Hey, it's working. Be happy.



It occurred to me that if this were a customers radio, I'd likely own
their home at this point...

More likely, they'd own your shop.

--Winston

So I've replaced all the original transistors, resoldered the
transistor cans, (grounds) and reset the bias with R22 to -1.18V with
7.50V applied to the battery connector. That bias voltage however
rises to -1.33V when the supply is boosted up to 9.0V. So as I
expected, it seems that the supply voltage does make a small
difference in bias. Does anyone else have any theories as to what
Grundig may have had in mind when they specified that bias as well as
the other circuit voltages? Was it with 7.50V applied or 9.0V? Lenny

There's a note on the schematic that they're measured with a battery
voltage of 7.5V. Using a vaccum tube volt-meter, which you might have
some difficulty obtaining now

I'm surprised at the variation in bias with supply voltage. I would have
expected it to be quite insensitive.

Sylvia.

 

[Winston]

Sylvia Else wrote:

On 12/03/2012 12:05 PM, klem kedidelhopper wrote:

(...)

Was it with 7.50V applied or 9.0V? Lenny

There's a note on the schematic that they're measured with a battery voltage of 7.5V.

That looks like a typo.

R46 will drop 100 mV for every milliampere of battery current.

The only way to get the specified rail voltage of
7.0 V at 20 mA (Medium Wave operation) is with a
battery voltage of 9.0. Similarly, it takes 8.95 V
of battery voltage to get 6.75 V at 22 mA on
the rail, specified for FM operation.

Using a vaccum tube volt-meter,
which you might have some difficulty obtaining now

I'm willing to believe that a modern multimeter is more
than sufficient for these measurements. My Fluke 189
has an input impedance of 10 M. I'm not too concerned
about the additional 82 nA it costs to use, for a 9 V measurement.




--Winston

 

[William Sommerwerck]

I'm guessing that the 7.5V specs are for the lowest voltage the designers
felt gave acceptable performance.

Regardless, the important thing is the /relative/ voltages on a device's
terminals.

The base-emitter junction is forward-biased, about 0.3V for Ge devices, 0.6V
for Si. The base-collector junction is reverse-biased.

 

[Winston]

William Sommerwerck wrote:

I'm guessing that the 7.5V specs are for the lowest voltage the designers
felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and 'battery +',
*not between 'battery -' and 'battery +'*.

Unfortunately, they call 'power rail voltage' and 'battery
voltage' the same thing. They are different by 2 V in MW mode!



--Winston

 

[William Sommerwerck]

"Winston" <Winston@Bigbrother.net> wrote in message
news:jjku9b02fns@news6.newsguy.com...

William Sommerwerck wrote:

I'm guessing that the 7.5V specs are for the lowest voltage
the designers felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and "battery +",
not between "battery -" and "battery +".

Unfortunately, they call "power rail voltage" and "battery voltage"
aren't the same thing. They are different by 2V in the MW model.

While we're at it... It's perfectly normal for amplifier stages -- tube or
transistor, in any kind of device -- to be fed through a small resistor,
with a largish capacitor to ground. This "decouples" the stage from the
power supply, to prevent feedback. The resistor /is not/ present to reduce
the power-supply voltage.

 

[Winston]

William Sommerwerck wrote:

"Winston"<Winston@Bigbrother.net> wrote in message
news:jjku9b02fns@news6.newsguy.com...
William Sommerwerck wrote:

I'm guessing that the 7.5V specs are for the lowest voltage
the designers felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and "battery +",
not between "battery -" and "battery +".

Unfortunately, they call "power rail voltage" and "battery voltage"
[the same thing. They are different by 2 V in MW mode! ]

aren't the same thing. They are different by 2V in the MW model.

Thanks for fixing that William, but that's not what I
said or meant.

The MW and FM models are the same radio model.

When testing in Medium Wave *mode* the radio
requires 7.5 V between system ground and the power rail and is
specified to draw ca 20 mA. In FM *mode*, the radio is specified
to draw ca 22 mA from that same 7.5 V rail.

This is *not* the same as a 'battery voltage' of 7.5 V.
Our friends at Grundig have the same phrase to describe
'rail voltage' and 'battery voltage', which are normally
ca ~2 V different on the 'return' side.

I now understand that it makes perfect sense to attach our service
supply between 'system ground' and 'power rail' so that the
'system ground' can be bonded to earth ground via the power
supply, for safety. This is not the same as attaching the
supply across the battery, however.

While we're at it... It's perfectly normal for amplifier stages -- tube or
transistor, in any kind of device -- to be fed through a small resistor,
with a largish capacitor to ground.

Yup. In this case, they are decoupling the final audio
stage from the rest of the radio.

This "decouples" the stage from the
power supply, to prevent feedback. The resistor /is not/ present to reduce
the power-supply voltage.

Yet it does, by about 2 V from the battery to power rail.

--Winston

 

[Winston]

Winston wrote:

(...)

'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.

Mia Culpa! The specification on the schematic is not
a *range* of acceptable rail voltages, it is a declaration
that the rail voltage must be +7 V in MW mode or +6.75 V
in FM mode, (An inch to the right, they re-declare both
at 7.5 V on the rail!)

I'd go with 7.5 V between ground and the power rail.
I'd leave 'battery minus' floating.


--Winston

 

[klem kedidelhopper]

On Mar 12, 10:29 am, Winston <Wins...@Bigbrother.net> wrote:

William Sommerwerck wrote:
"Winston"<Wins...@Bigbrother.net>  wrote in message
news:jjku9b02fns@news6.newsguy.com...
William Sommerwerck wrote:

I'm guessing that the 7.5V specs are for the lowest voltage
the designers felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and "battery +",
not between "battery -" and "battery +".

Unfortunately, they call "power rail voltage" and "battery voltage"

[the same thing. They are different by 2 V in MW mode! ]

aren't the same thing. They are different by 2V in the MW model.

Thanks for fixing that William, but that's not what I
said or meant.

The MW and FM models are the same radio model.

When testing in Medium Wave *mode* the radio
requires 7.5 V between system ground and the power rail and is
specified to draw ca 20 mA.  In FM *mode*, the radio is specified
to draw ca 22 mA from that same 7.5 V rail.

This is *not* the same as a 'battery voltage' of 7.5 V.
Our friends at Grundig have the same phrase to describe
'rail voltage' and 'battery voltage', which are normally
ca ~2 V different on the 'return' side.

I now understand that it makes perfect sense to attach our service
supply between 'system ground' and 'power rail' so that the
'system ground' can be bonded to earth ground via the power
supply, for safety.  This is not the same as attaching the
supply across the battery, however.

While we're at it... It's perfectly normal for amplifier stages -- tube or
transistor, in any kind of device -- to be fed through a small resistor,
with a largish capacitor to ground.

Yup.  In this case, they are decoupling the final audio
stage from the rest of the radio.

This "decouples" the stage from the
power supply, to prevent feedback. The resistor /is not/ present to reduce
the power-supply voltage.

Yet it does, by about 2 V from the battery to power rail.

--Winston

I was using my RCA Senior Voltohmyst in the beginning. It has either a
10 or 11M impedance, however I built it from a kit I think in 1964. So
being almost 50 years old it's calibration could have been suspect. I
then switched to my Fluke digital. In any case I found that the
readings on both were very close anyway. (I don't use the VTVM much
anymore unless I get an old tube set in here to work on).

My initial reading on R24 before I made any adjustments, with 7.50V
applied to the battery terminals was 1.00V. That voltage rose to
3.60V when C38 would fail. Remember, (after replacing C38) that I
noted an approximate .015 V rise in VR24 when I increased the supply
from 7.50V to 9.0V. Assuming the engineers meant for this voltage to
be set with 9.0V applied, then perhaps I was reading what would be a
perfect bias point (with 7.50V applied), as measured on VR24
initially. It would be nice to know for certain after such an
exercise, but at this point I doubt very much that even someone at
Grundig would be able to shed any further light on this. But then what
you're saying makes perfect sense too Winston. I'm just really
surprised at the ambiguity of the statement on the schematic. In any
event there seems to be an amount of latitude available here, and
given (and I'm assuming) that the radio appears to have been working
that way for many years, perhaps it's a waste of time to fret over .
015V. Maybe I'll set it somewhere in between, enjoy my radio once
again and step back into reality....That would make my wife, who has
failed to see the sense in fixing a 40 year old radio very happy
indeed. Lenny

 

[Winston]

klem kedidelhopper wrote:

On Mar 12, 10:29 am, Winston<Wins...@Bigbrother.net> wrote:
William Sommerwerck wrote:
"Winston"<Wins...@Bigbrother.net> wrote in message
news:jjku9b02fns@news6.newsguy.com...
William Sommerwerck wrote:

I'm guessing that the 7.5V specs are for the lowest voltage
the designers felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and "battery +",
not between "battery -" and "battery +".

Unfortunately, they call "power rail voltage" and "battery voltage"

[the same thing. They are different by 2 V in MW mode! ]

aren't the same thing. They are different by 2V in the MW model.

Thanks for fixing that William, but that's not what I
said or meant.

The MW and FM models are the same radio model.

When testing in Medium Wave *mode* the radio
requires 7.5 V between system ground and the power rail and is
specified to draw ca 20 mA. In FM *mode*, the radio is specified
to draw ca 22 mA from that same 7.5 V rail.

This is *not* the same as a 'battery voltage' of 7.5 V.
Our friends at Grundig have the same phrase to describe
'rail voltage' and 'battery voltage', which are normally
ca ~2 V different on the 'return' side.

I now understand that it makes perfect sense to attach our service
supply between 'system ground' and 'power rail' so that the
'system ground' can be bonded to earth ground via the power
supply, for safety. This is not the same as attaching the
supply across the battery, however.

While we're at it... It's perfectly normal for amplifier stages -- tube or
transistor, in any kind of device -- to be fed through a small resistor,
with a largish capacitor to ground.

Yup. In this case, they are decoupling the final audio
stage from the rest of the radio.

This "decouples" the stage from the
power supply, to prevent feedback. The resistor /is not/ present to reduce
the power-supply voltage.

Yet it does, by about 2 V from the battery to power rail.

--Winston

I was using my RCA Senior Voltohmyst in the beginning. It has either a
10 or 11M impedance, however I built it from a kit I think in 1964. So
being almost 50 years old it's calibration could have been suspect. I
then switched to my Fluke digital. In any case I found that the
readings on both were very close anyway. (I don't use the VTVM much
anymore unless I get an old tube set in here to work on).

They were great tools in their day.
I had a PACO and lusted after a Voltohmyst.
http://www.glowbug.nl/valve/Paco-V70.html

My initial reading on R24 before I made any adjustments, with 7.50V
applied to the battery terminals was 1.00V.

Yup. Grundig said "Battery Voltage" but they meant
"Rail Voltage". The two are different. By 2 V!

That voltage rose to
3.60V when C38 would fail. Remember, (after replacing C38) that I
noted an approximate .015 V rise in VR24 when I increased the supply
from 7.50V to 9.0V. Assuming the engineers meant for this voltage to
be set with 9.0V applied, then perhaps I was reading what would be a
perfect bias point (with 7.50V applied), as measured on VR24
initially. It would be nice to know for certain after such an
exercise, but at this point I doubt very much that even someone at
Grundig would be able to shed any further light on this.

I think we have the straight info. I bet the bias when
set with 7.5 V *on the rail* would not drift very much
at all when the radio is powered from a 9 V battery.

But then what
you're saying makes perfect sense too Winston. I'm just really
surprised at the ambiguity of the statement on the schematic.

Someone should write a Grundig Schematic Decoder!

They do present a lot of information but it does take time
to digest the hieroglyphics in order to translate.

In any
event there seems to be an amount of latitude available here, and
given (and I'm assuming) that the radio appears to have been working
that way for many years, perhaps it's a waste of time to fret over .
015V.

I agree. It is probably as close as it needs to be.

Maybe I'll set it somewhere in between, enjoy my radio once
again and step back into reality....That would make my wife, who has
failed to see the sense in fixing a 40 year old radio very happy
indeed.

I agree. There are plenty of 40 year old electronics
to repair everywhere. You should be very pleased to
have your nifty radio back!

--Winston

 

[klem kedidelhopper]

On Mar 12, 11:59 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:

On Mar 12, 10:29 am, Winston <Wins...@Bigbrother.net> wrote:









William Sommerwerck wrote:
"Winston"<Wins...@Bigbrother.net>  wrote in message
news:jjku9b02fns@news6.newsguy.com...
William Sommerwerck wrote:

I'm guessing that the 7.5V specs are for the lowest voltage
the designers felt gave acceptable performance.

I feel that Grundig assumed the service person would connect
their bench supply between rail ground and "battery +",
not between "battery -" and "battery +".

Unfortunately, they call "power rail voltage" and "battery voltage"

[the same thing. They are different by 2 V in MW mode! ]

aren't the same thing. They are different by 2V in the MW model.

Thanks for fixing that William, but that's not what I
said or meant.

The MW and FM models are the same radio model.

When testing in Medium Wave *mode* the radio
requires 7.5 V between system ground and the power rail and is
specified to draw ca 20 mA.  In FM *mode*, the radio is specified
to draw ca 22 mA from that same 7.5 V rail.

This is *not* the same as a 'battery voltage' of 7.5 V.
Our friends at Grundig have the same phrase to describe
'rail voltage' and 'battery voltage', which are normally
ca ~2 V different on the 'return' side.

I now understand that it makes perfect sense to attach our service
supply between 'system ground' and 'power rail' so that the
'system ground' can be bonded to earth ground via the power
supply, for safety.  This is not the same as attaching the
supply across the battery, however.

While we're at it... It's perfectly normal for amplifier stages -- tube or
transistor, in any kind of device -- to be fed through a small resistor,
with a largish capacitor to ground.

Yup.  In this case, they are decoupling the final audio
stage from the rest of the radio.

This "decouples" the stage from the
power supply, to prevent feedback. The resistor /is not/ present to reduce
the power-supply voltage.

Yet it does, by about 2 V from the battery to power rail.

--Winston

I was using my RCA Senior Voltohmyst in the beginning. It has either a
10 or 11M impedance, however I built it from a kit I think in 1964. So
being almost 50 years old it's calibration could have been suspect. I
then switched to my Fluke digital. In any case I found that the
readings on both were very close anyway. (I don't use the VTVM much
anymore unless I get an old tube set in here to work on).

My initial reading on R24 before I made any adjustments, with 7.50V
applied to the battery terminals was 1.00V.  That voltage rose to
3.60V when C38 would fail. Remember, (after replacing C38) that I
noted an approximate  .015 V rise in VR24 when I increased the supply
from 7.50V to 9.0V. Assuming the engineers meant for this voltage to
be set with 9.0V applied, then perhaps I was reading what would be a
perfect bias point (with 7.50V applied), as measured on VR24
initially. It would be nice to know for certain after such an
exercise, but at this point I doubt very much that even someone at
Grundig would be able to shed any further light on this. But then what
you're saying makes perfect sense too Winston. I'm just really
surprised at the ambiguity of the statement on the schematic. In any
event there seems to be an amount of latitude available here, and
given (and I'm assuming) that the radio appears to have been working
that way for many years, perhaps it's a waste of time to fret over .
015V. Maybe I'll set it somewhere in between, enjoy my radio once
again and step back into reality....That would make my wife, who has
failed to see the sense in fixing a 40 year old radio very happy
indeed.  Lenny

Well I couldn't resist, so to take this a bit further I checked the
power supply supplied with the radio. It is rated at 9.00V .200A. The
no load voltage is 9.50V. With it connected to the radio and with the
radio playing softly its output drops to 9.25V. In looking at the
schematic again and rereading the statement a few more times I now do
believe that in spite of the ambiguity, the original intention was to
supply 7.50 V to the battery terminals, however reference all
adjustments and voltages to the positive side of C59, (system ground).
So I did that and set the bias on FM to -1.18V. (AF126 I E) I then
recorded the following voltages:

Voltage readings
Test point Radio working:
------------------- --------------------

E. AF178 -1.15V
B. AF178 -1.48V
E. AF124 -1.14V
B. AF124 -1.37V
E. AF121 -0.90V
B. AF121 -1.24V
E. AF126 (1) -1.18V
B. AF126 (1) -1.47V
E. AF126 (II) -1.14V
B. AF126 (II) -1.34V

The voltage across C59 is 6.65V
So now although the radio has been working fine on both AM and FM, I
notice that the first two stages are reading a bit high. I wonder if I
may have another leaky cap. I was looking at possibly C12, C19 and
C32. Assuming I haven't driven everyone nuts with this project yet I
wonder what is the general consensus with this new revelation is?
Lenny