Grundig AM/FM portable "Transistor 305" troubleshooting

  • Thread starter klem kedidelhopper
  • Start date
klem kedidelhopper wrote:
On Mar 12, 11:59 am, klem kedidelhopper<captainvideo462...@gmail.com
Click to expand...
(...)

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:
Click to expand...
Here, I added a Vnom column.

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

E. AF178 -1.15V -0.85
B. AF178 -1.48V -1.15
E. AF124 -1.14V -0.94
B. AF124 -1.37V -1.12
E. AF121 -0.90V -0.85 (MW) -0.60 (FM)
B. AF121 -1.24V -1.05 (MW) -0.95 (FM)
E. AF126 (1) -1.18V -1.18 (MW) -1.15 (FM)
B. AF126 (1) -1.47V -1.45 (MW) -1.4 (FM)
E. AF126 (II) -1.14V -1.05 (MW) -1.0 (FM)
B. AF126 (II) -1.34V -1.33 (MW) -1.0 (FM)

The voltage across C59 is 6.65V
Click to expand...
You are testing at Vrail = 6.65 V?

Grundig says "don't bother warming up the VTVM unless
Vrail ==7.5 V" ( I heard them. Really I did. :)

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.
Click to expand...
The little 'K' symbol next to these three apparently
denotes a ceramic cap. These 500 V units could become
extremely leaky at < 2 V I suppose.

I wouldn't bet that way, however.


There are lots more things that need your attention more
than your beloved radio. Personally, I think that at this
rate, in another 30 days, you will become borderline
obsessive. :)

My advice: Button it up and listen to it while doing one or more:

Clean or replace the sacrificial anode in your water heater

Do an oil change on your car

Flush and fill your car radiator

Rotate your tires

Replace the transmission fluid in your car
(Clean your funnel and flush with clean ATF first!)

Grab a basket and fill it with stuff from the back seat
and trunk. Neatly put away, toss or donate the contents
of the basket.

Shampoo car carpets

Diagnose that rattle in your clothes dryer

Vacuum out your dryer exhaust vent

Clean your gutters

Replace clogged rafter end vents with new ones

Replace the nasty 'wiring' job in the garage with
real Romex or conduit as code permits.

Install a chimney - mount 'Over The Air' antenna and cancel
your cable TV subscription

Scavenge stuff out of one room or garage that you
honestly will never need and give it to your local
Freecycler

Buy a little microcontroller board and teach yourself
assembly language. Make a robot.

etc. etc. :)


--Winston
 
klem kedidelhopper wrote:

(...)

Wow! I'll never complain about my wife nagging me again. I think
you've covered everything. Lenny
Click to expand...
:)

--Winston<--Nag, whine, nag, nag, nag.
 
On Mar 12, 5:17 pm, Winston <Wins...@Bigbrother.net> wrote:
klem kedidelhopper wrote:
On Mar 12, 11:59 am, klem kedidelhopper<captainvideo462...@gmail.com

(...)

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:

Here, I added a Vnom column.









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

    E. AF178                -1.15V                 -0.85
    B. AF178                -1.48V         -1.15
    E. AF124                -1.14V         -0.94
    B. AF124                -1.37V         -1.12
    E. AF121                -0.90V         -0.85 (MW) -0.60 (FM)
    B. AF121                -1.24V         -1.05 (MW) -0.95 (FM)
    E. AF126 (1)           -1.18V          -1.18 (MW) -1.15 (FM)
    B. AF126 (1)           -1.47V          -1.45 (MW) -1.4 (FM)
    E. AF126 (II)           -1.14V         -1.05 (MW) -1.0 (FM)
    B. AF126 (II)           -1.34V         -1.33 (MW) -1.0 (FM)

The  voltage across C59 is 6.65V

You are testing at Vrail = 6.65 V?

Grundig says "don't bother warming up the VTVM unless
Vrail ==7.5 V"  ( I heard them.  Really I did.  :)

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.

The little 'K' symbol next to these three apparently
denotes a ceramic cap. These 500 V units could become
extremely leaky at < 2 V I suppose.

I wouldn't bet that way, however.

There are lots more things that need your attention more
than your beloved radio.  Personally, I think that at this
rate, in another 30 days, you will become borderline
obsessive.  :)

My advice: Button it up and listen to it while doing one or more:

        Clean or replace the sacrificial anode in your water heater

        Do an oil change on your car

        Flush and fill your car radiator

        Rotate your tires

        Replace the transmission fluid in your car
        (Clean your funnel and flush with clean ATF first!)

        Grab a basket and fill it with stuff from the back seat
        and trunk.  Neatly put away, toss or donate the contents
        of the basket.

        Shampoo car carpets

        Diagnose that rattle in your clothes dryer

        Vacuum out your dryer exhaust vent

        Clean your gutters

        Replace clogged rafter end vents with new ones

        Replace the nasty 'wiring' job in the garage with
        real Romex or conduit as code permits.

        Install a chimney - mount 'Over The Air' antenna and cancel
        your cable TV subscription

        Scavenge stuff out of one room or garage that you
        honestly will never need and give it to your local
        Freecycler

        Buy a little microcontroller board and teach yourself
        assembly language.  Make a robot.

        etc. etc.   :)

--Winston
Click to expand...
Wow! I'll never complain about my wife nagging me again. I think
you've covered everything. Lenny
 
On Mar 12, 8:19 pm, Winston <Wins...@Bigbrother.net> wrote:
klem kedidelhopper wrote:

(...)

Wow! I'll never complain about my wife nagging me again.  I think
you've covered everything. Lenny

:)

--Winston<--Nag, whine, nag, nag, nag.
Click to expand...
I never thought of myself as being obsessive compulsive. In fact I've
been contemplating that for months and have finally decided that I'm
not...

I put the radio together last night. I'm listening to it right now.
It's nice to be able to "see" my bench again, and be done with this
project. It seems to play fine on both bands, in spite of the slight
difference in readings on the front end. I'm not going to worry about
that or the exact bias point for that matter. I have all my notes and
that's a project for another day, (maybe). I'm grateful that it's
working, and so well, and for all the friends who've helped me along
the way.

You'll have to excuse me now though. I have to go build a garage, so
that I can clean it out. Thanks again to everyone.
Best regards, Lenny

PS. I'll let you know when the next Philco Predicta walks in here...
 
klem kedidelhopper wrote:
On Mar 12, 8:19 pm, Winston<Wins...@Bigbrother.net> wrote:
klem kedidelhopper wrote:

(...)

Wow! I'll never complain about my wife nagging me again. I think
you've covered everything. Lenny

:)

--Winston<--Nag, whine, nag, nag, nag.

I never thought of myself as being obsessive compulsive. In fact I've
been contemplating that for months and have finally decided that I'm
not...
Click to expand...
Heh! Good one!

I put the radio together last night. I'm listening to it right now.
It's nice to be able to "see" my bench again, and be done with this
project. It seems to play fine on both bands, in spite of the slight
difference in readings on the front end. I'm not going to worry about
that or the exact bias point for that matter. I have all my notes and
that's a project for another day, (maybe). I'm grateful that it's
working, and so well, and for all the friends who've helped me along
the way.
Click to expand...
Especially Sylvia and Franc that got you pointed in
the proper direction.

You are now the World Expert on the Grundig Transistor 305.
Congratulations!

You'll have to excuse me now though. I have to go build a garage, so
that I can clean it out. Thanks again to everyone.
Best regards, Lenny

PS. I'll let you know when the next Philco Predicta walks in here...
Click to expand...
Hoo Boy. Cannot wait for that.

--Winston :)
 
Winston wrote:
klem kedidelhopper wrote:
?
? PS. I'll let you know when the next Philco Predicta walks in here...

Hoo Boy. Cannot wait for that.
Click to expand...

They show up on news:rec.antiques.radio+phono from time to time.


--
You can't have a sense of humor, if you have no sense.
 
On Mon, 12 Mar 2012 15:26:38 +1100, Sylvia Else <sylvia@not.here.invalid>
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

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.
Click to expand...
Please to explain just why. As i don't think any possible intermittent
failure of C38 will explain the voltages seen.

?-)
 
On 17/03/2012 1:35 PM, josephkk wrote:
On Mon, 12 Mar 2012 15:26:38 +1100, Sylvia Else<sylvia@not.here.invalid
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

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.

Please to explain just why. As i don't think any possible intermittent
failure of C38 will explain the voltages seen.

?-)
Click to expand...
Such a crack would certainly stop the radio from working, but there
would be nothing left to pull the emitters positive. They'd go to
ground, pulled there through R26. That's not what the OP observed.

The loss of the emitter-base currents (those junctions now being reverse
biased) would cause the base voltages to drop somewhat, but not by
anything like the amounts seen.

I have my own doubts about C38, notwithstanding the OP's apparently
successful repair, but that's a separate issue.

Sylvia.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top