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


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