[R-390] Saturday's Line & Local Report

[Craig Heaton]

Good evening Charles,

To all, once again I do appreciated the help and suggestions, really!
Proceeding in an orderly, logical way is only one point of view. Your
suggestion of using a scope connected between pin 7 of C603 and a resistor
(forget which one) is a great idea. We have valid data, there is audio
there! Last night, once again the wiring was checked. Starting from the cap
C603, the connections thru pins 1,3,5,& 7 are good. They are connected to
the correct spots. All the negative leads of the cap connect to pin one (1).
There is a short wire directly from pin one (1) of the socket for C603 to
the AF chassis. Either from P120 or P119, the AF chassis is grounded to the
main chassis. So if C603 should bypass audio to ground at that spot, the
path is there. Might add checked a lot of wire and components in the AF last
night, didn't find anything. It's not going to get better this year.   

Today's little test gives me confidence all is well in the IF, time to move
on. Don't be like a deer froze by the headlights of a car. Do something. 

So do I order a high temp cap or a general purpose cap????? Newark isn't
stocking like they use to, I have an account with
Mouser........647-UBT2V330MHD their part number for a Nichicon and will fit
in the can. Not going to mount under the chassis, no air flow. Xicon is not
a candidate.

Pllleeeeaaasse.............let's not start a cap battle! 

Regards,
Craig 





Like Bob and Tisha, I am concerned that you are not proceeding in an
orderly, logical way and are not making use of all the data that you are
collecting as you go.  This can only lead to frustration and wasted effort.
Module swapping is a way to EXCLUDE modules as the source of a problem as
much as it is a way to identify bad modules.  Some of the data you have
collected seems to indicate that the problem is NOT IN THE AMELCO IF OR AF
MODULES AT ALL.  Thus the suggestion to swap modules again, to be sure.
Note that it is just as important to swap the questionable modules into the
known good radio as it is to swap the known good modules into the radio with
the problem.

If swapping the Moto AF module into the Amelco radio (which you say you have
done) does not fix the problem (which you say it doesn't), it strongly
suggests that the Amelco AF module is not the source of the problem, because
if the problem is in a module, we expect it to follow that module.  You
would confirm the "Amelco AF module is not the source of the problem"
hypothesis by installing it in the Moto radio (which you do not say you have
done).  If you do, and the Moto radio works fine with the Amelco AF module,
then THE PROBLEM IS NOT INTERNAL TO THE AMELCO AF MODULE and you can stop
looking for it there.

The same applies to IF modules.  You say putting the Moto IF module into the
Amelco radio does not fix the problem in the Amelco radio.  You would
confirm this by putting the Amelco IF module into the Moto radio.  If it
works fine there, THE PROBLEM IS NOT INTERNAL TO THE AMELCO IF MODULE and
you can stop looking for it there.

Until you do the experiment and find otherwise, it appears from what you
have said so far this would indeed be the case.  So, the path to greatest
information for the least work is:  (1) swap the AF modules BOTH WAYS (Moto
AF into Amelco radio, Amelco AF into Moto radio).  If the Amelco radio still
has the problem and the Moto radio still works fine, leave the AF modules
where they are and (2) swap the IF modules both ways (Moto IF into Amelco
radio, Amelco IF into Moto radio).  If the Amelco radio still has the
problem and the Moto radio still works fine, THE PROBLEM IS NOT INTERNAL TO
THE AMELCO AF OR IF MODULES.  Again, from what you have said so far (Moto AF
module in the Amelco radio does not cure the Amelco radio, Moto IF module in
the Amelco radio does not cure the Amelco radio), we expect that this will
be the case.

That may be a fair amount of work, but if you do it and the results are as
above, you can QUIT LOOKING FOR THE PROBLEM INSIDE THE AMELCO AF AND IF
MODULES.  Think how much work that would save you.  (If you had done that
first, and those were the results, you wouldn't have had to do any of the
work you have done these past several years and could have concentrated your
efforts on looking elsewhere for the problem.)

SO, if the problem is not internal to the Amelco AF or IF modules, where can
it be??  The next most likely suspects would be grounding and the wiring
harness.  For example, if you have audio at the junction of of R606 and the
AF B+ choke (L603), yet the capacitors in
C603 appear to be good, it could be because the negative end of C603 is not
properly grounded due to a faulty ground to the main chassis.  Since you
have already found a number of issues with the harness, further problems in
that area should not be a surprise.

Best regards,

Charles


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