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klem kedidelhopper klem kedidelhopper is offline
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Default Grundig AM/FM portable "Transistor 305" troubleshooting

On Mar 9, 4:45*pm, amdx 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