A fellow objected to my posting somewhat strongly as follows:

That's just not how ADF circuits typically work. I think you're
making all this up. Otherwise, you'd understand how the "oscillators"
work when they're commonly digital PLL's, and that if a receiver did
alignment, it sure ain't gonna be due to "drifting tantalum caps," as
if they are especially prone to do that in the first place.



O.K. Chill suit "ON".

I believe we are talking about 25 year old radios. There ain't no
digital ANYTHING in there (except maybe some units that had digital LED
segmented or incandescent segmented frequency displays and some simple
CMOS gate packages to drive them).

As I said, I don't repair radios for a living. Sorry if your opinion is
different. If anyone can explain analog AM radio alignment and theory of
operation in better laymen's terms, I'm all ears.

However, the 3 folks I deal with that do repair old radios for a living
report that, in their experience, tantalum caps ARE more prone to
leakage/failure with age than other types (electrolytics, mylars, etc.).
Your experience may be different. If anyone has actual testing and
failure data, please chime in.

A few titles in the "Maintenance" section for my ADF:
* Oscillator Alignment
* IF Alignment
* Receiver Alignment
* ADF alignment.

Leaking caps are not the problem? Maybe, but the odds are they
contribute to some problems. Maybe I was just on a streak when we had to
replace several of them in my unit to get it to work properly. Sorry,
one was actually shorted, not leaking.

If the caps were not leaking, resistors drifting/burning, and
transistors changing conductance across their junctions (all due to heat
and age), why would any of this be necessary? Does it matter WHICH
component type actually causes the most trouble? I think not.

The fellow was asking why his receiver did not point correctly. I tried
to relay the message that many of these old buzzards needed the
equivalent of a "tune up" to get them working properly. The posting above
suggests that I was trying to sell him some kind of deception. Not so.
Making it up? Let's just say that my efforts may be imperfect in this
case. I cannot be an expert in everything. Hell, I ain't an expert in
ANYTHING that I can think of. I only fixed electronic gear
for a couple of years, and that was a LOOOOONG time ago.

I was not volunteering to fix his receiver. So, I have no duty to be
spot on in any diagnosis or explanation of the theory of operation. I
offered my limited experience with the caveat that this ain't my line of
work any more.

I merely suggested he get the thing fixed. Sorry if my imperfect
explanation of the problem causes anyone heartburn. My advice was worth
every penny he paid (BIG SILLY GRIN)

Good Luck,
Mike


P.S.
Post from another fellow on the thread:
"I had some similar problems with the Narco ADF 841. It wouldn't lock
onto anything more than a few miles away until the radio had been on for
an hour or so. I sent it in for repair, the shop tested it and replaced
two capacitors, and now it works perfectly."

Please note the offending devices - capacitors, I believe. Won't work
unless REALLY warmed up = LEAKING. Maybe I am not that crazy after all...


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