On Mar 7, 12:06*am, Winston 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/Gru...0schematic.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