klem kedidelhopper wrote:
On Mar 9, 4:45 pm, 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

It'd be great if C38 turned out to be our leaker, current-wise.

I'm still curious why the increased base current through
R21 (949 uA) is not completely apparent as an increased current in
the resistor that is in series with it, R28 (only 130 uA more,
not 949 uA more). Our increased current isn't going through R22
because during the failure, current through R22 *decreases*.



Resistance Eworking Iworking Enotworking Inotworking Edifference Idifference
R28 15000 0.07800000 0.00000520 2.00000000 0.00013333 1.92200000 0.00012813
R21 2200 0.01200000 0.00000545 2.10000000 0.00095455 2.08800000 0.00094909
R29 330 0.00670000 0.00002030 0.00110000 0.00000333 -0.00560000 -0.00001697
R22 15000 5.80000000 0.00038667 2.30000000 0.00015333 -3.50000000 -0.00023333
R26 180000 5.41000000 0.00003006 2.60000000 0.00001444 -2.81000000 -0.00001561
R25 10000 0.05700000 0.00000570 0.10500000 0.00001050 0.04800000 0.00000480
R24 820 1.00000000 0.00121951 3.70000000 0.00451220 2.70000000 0.00329268

--Winston