On May 20, 3:21*pm, klem kedidelhopper
wrote:
I have a Grundig "Transistor 305" portable radio. It uses germanium
transistors. I've had this thing for over forty years and although I
don't use it often it has been a nice radio. In 1971 I replaced the
transistor in the FM detector circuit and I have had no problems with
it until just recently. *Last month I spent three days in the hospital
and I brought the Grundig with me. I noticed that after it was on for
about a half hour it would start to cut out. I turned it off and then
later turned it on again, and after a period of time it happened
again. After several similar episodes I stopped using it. I wondered
about some type of interference from the hospital but that was wishful
thinking. In any case being in no position to test it I decided to
just put it away. Yesterday I put it on the bench and took a look at
it. Sure enough after a brief time it cut out again. I injected a
signal, (my finger on a small screwdriver) onto the wiper of the
volume control and ascertained that there is nothing wrong up to the
speaker. So now I need to get into the IF's and detector. My problem
is my old signal generators are not working and all I can come up with
for 10.7MHZ. is a CW signal out of my MFJ249 SWR meter. The MFJ puts
out a clean signal however it is CW, and it's amplitude is not
adjustable. I don't think that an unmodulated signal would be a
problem in this application but I don't know what the amplitude of the
MFJ is and I would hate to blow up an otherwise good IF amplifier with
an excessive signal. I''m admittedly a bit rusty having not trouble
shot an IF amplifier/detector circuit in many years so does anyone
have a feel for how I might signal trace this radio with what I have
on hand? *Thanks very much for any advice. Lenny

I would first look at mechanical failure of the connections. ...PCB/
traces/etc.

Especially around the FM Detector area where you heat shocked the PCB
when changing that transistor.

I know it's hard to believe battery can heat that much but with age on
a PCB, you'd be surprised. Ever try cold spray when radio failed?