"Mr. Land" wrote in message
...
On Dec 1, 4:25 pm, "Arfa Daily" wrote:
"EADGBE" wrote in message

...



(Please forgive me if I say anything dumb in this post...I am a home
enthusiast who is experienced at working on amplifiers, tape decks,
and turntables, but I haven't really worked on tuners at all.....)

As you all may recall, my Technics SA-400 receiver's "FM Stereo"
indicator would not light up, even when receiving any of the strong FM
stations in my area.

A few folks kindly told me how to adjust the VCO circuit. I used my
frequency counter and hooked it up via a 100k resistor to the
appropriate test point and was able to adjust the VCO perfectly to
19kHz.

For a few weeks, the receiver worked great. I was able to get "FM
Stereo" indicator to light AND could plainly hear the stereo image of
my favorite FM station.

But now, the same problem has happened again. The "FM Stereo"
indicator does not light and I do NOT hear stereo.

I was able to verify that the "FM Stereo" light DOES work.
Interestingly, the last time the "FM Stereo" light worked, I was
dialing in a station, the light came on for half a second, then went
out.

It's as if the receiver is TRYING to give me FM stereo, but for some
reason cannot.

QUESTION: What procedure(s) do I need to do to align the FM tuner so
this problem won't happen again? I have a frequency counter, a signal
generator (20Hz to 20kHz), and a Nakamichi T-100 audio analyzer. My
scope, unfortunately, is non-functional at the moment.

Many thanks in advance........

It is *extremely* unlikely that the fault is due to any of the front end
alignment being wrong. It just doesn't happen.

Why is it unlikely? I'm not familiar with this receiver, but if it is
as old as it
sounds, and has an RF tuner using the old finned air capacitors, these
RF
sections almost always benefit from tweaking. I can't remember a
single
one that didn't benefit when we fine-tuned the caps and coils in the
RF section.

I'm not disagreeing with you, just interested in the details.

Also for the OP, I didn't see it mentioned in this thread, but be
aware if
your receiver has the old "can" tuning transformers, some of these
actually
have two slugs in them, upper and lower.

Cheers.

EeAeDdGgBbEx (darn, broke a string again)

I think you misunderstood the intention of what I was saying. I don't
disagree that old receivers can often be 'improved' - at least on the face
of it - by tweaking up the front end. I was just saying that this particular
fault, which is a lack of stereo decoding irrespective of how strong the
received station is, is unlikely to be as a result of anything prior to the
demodulator being out of alignment. I suppose it is just conceivable that if
the IFs were sufficiently wrongly stagger tuned, you might just be able to
screw up the pilot tone recovery, but I think that if it was that badly
misaligned, it would be unlikely that it would ever work, which it does
sometimes, and that lack of stereo decoding would be the most noticable
symptom. As the OP says that he is not skilled with receivers, and alignment
was being suggested by other posters as being a possible cause, I did not
want him to go in with random twiddling, which would quite possibly compound
the problem.

I don't think that I can recall ever having a stereo decoding issue with one
of these old receivers, that was not down to discriminator alignment, pilot
tone PLL misalignment, or a genuine faulty component around the decoder
chip. Would you agree with that analysis ? :-)

Arfa