[EADGBE]

(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........

[Mike Rivers]

On Dec 1, 9:30 am, EADGBE wrote:

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.

There are a whole bunch of alignment adjustments and you need to go
through the whole procedures. You'll need an RF signal generator,
usually a sweep generator for most FM alignment procedures. This isn't
something you can do at home with what you have.

You really need a service manual. I didn't find Technics SA-400 in the
Sams Photofact , but I found this source that claims to have it:
http://www.analogalley.com/m_techni.htm
That'll tell you what you need and how to do it.

[William Sommerwerck]

I have a gut feeling that this problem is due to simple component drift, and
not to the need for a complete alignment.

Am I correct in assuming that resetting the VCO control restores stereo
reception? If so...

Try replacing the pot with a cermet trimmer. It should have better long-term
stability.

When I owned the Heath "Most-Accurate Clock", I had stability problems that
went away when I replaced the carbon calibration pots with cermet.

Just a thought.

[Stuart[_2_]]

I would echo what William posted. The fact that you were able to recover
stereo ops by tweaking the VCO just about verifies that all the other
adjustments are ok. And any good tech will tell you that indiscriminate
tuning is not for the faint of heart: it usually creates more problems and
is also hard to resist. I would go back, re-adjust the VCO to get the light
back for a period of time to verify the fact and then look for something
causing the VCO to drift. Caps, trimmers and xtals are always suspects.
Good luck. Stuart.

"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........

[Arfa Daily]

"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. The most likely cause is that
the recovered pilot tone level is too low for the PLL to successfully lock
to - hence the reason that when the VCO was readjusted to be spot on, it
just about managed to 'hang in there' for a couple of weeks. Low pilot tone
recovery is usually caused by the discriminator coil being slightly off
alignment. It can be far enough off for the pilot tone to be low, without
being bad enough for you to be able to hear the characteristic distortion of
the audio when the misalignment is severe. As a first move, I would try just
rocking the core of that coil, with an APPROPRIATE PLASTIC trimmer tool,
plus / minus a half turn from its current position.

Do not at this stage attempt to alter the alignment of any other coils in
the IF strip. Even with all of the appropriate test equipment, it is an art
that is not easily learnt in any other way than by long experience. Most
people who are experienced in IF alignment, can do it by 'feel' and watching
the tuning meter. I seldom resort to generators and other fancy gear, unless
someone has *really* been 'at' it, and thrown the alignment out so far that
a proper starting point needs to be re-established.

What's the full model number ? SA - 400 doesn't seem long enough. It's
usually SA - xx400. I might be able to find a manual if you still need one.
You can always mail me direct, off-group, if you want.

Arfa

[Michael A. Terrell]

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. The most likely cause is that
the recovered pilot tone level is too low for the PLL to successfully lock
to - hence the reason that when the VCO was readjusted to be spot on, it
just about managed to 'hang in there' for a couple of weeks. Low pilot tone
recovery is usually caused by the discriminator coil being slightly off
alignment. It can be far enough off for the pilot tone to be low, without
being bad enough for you to be able to hear the characteristic distortion of
the audio when the misalignment is severe. As a first move, I would try just
rocking the core of that coil, with an APPROPRIATE PLASTIC trimmer tool,
plus / minus a half turn from its current position.

Do not at this stage attempt to alter the alignment of any other coils in
the IF strip. Even with all of the appropriate test equipment, it is an art
that is not easily learnt in any other way than by long experience. Most
people who are experienced in IF alignment, can do it by 'feel' and watching
the tuning meter. I seldom resort to generators and other fancy gear, unless
someone has *really* been 'at' it, and thrown the alignment out so far that
a proper starting point needs to be re-established.

What's the full model number ? SA - 400 doesn't seem long enough. It's
usually SA - xx400. I might be able to find a manual if you still need one.
You can always mail me direct, off-group, if you want.

Arfa


'SA-400 [M]' & 'SA-400 [MC]' Are US and Canadian model numbers. I
have the manual that covers these models, but it's in storage right now.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

[EADGBE]

OK...so...this is weird...

I haven't been listening to my SA-400 for a few days, because I just
wasn't that enthused about listening to my garage sale find when I
know that it isn't performing right.

ANYWAY...So I decide to listen to it today while I'm doing some
cleaning up.

I switch it on, and lo and behold, the FM Stereo indicator is back on,
and I verified that it is indeed putting out FM stereo again!

What gives?

[Arfa Daily]

"EADGBE" wrote in message
...

OK...so...this is weird...

I haven't been listening to my SA-400 for a few days, because I just
wasn't that enthused about listening to my garage sale find when I
know that it isn't performing right.

ANYWAY...So I decide to listen to it today while I'm doing some
cleaning up.

I switch it on, and lo and behold, the FM Stereo indicator is back on,
and I verified that it is indeed putting out FM stereo again!

What gives?

Possibly temperature related ? Did you get the reply regarding discriminator
alignment, that I sent you in response to the mail you sent me direct
off-group ?

Arfa

[Arny Krueger]

"EADGBE" wrote in message

OK...so...this is weird...

I haven't been listening to my SA-400 for a few days,
because I just wasn't that enthused about listening to my
garage sale find when I know that it isn't performing
right.

ANYWAY...So I decide to listen to it today while I'm
doing some cleaning up.

I switch it on, and lo and behold, the FM Stereo
indicator is back on, and I verified that it is indeed
putting out FM stereo again!

What gives?

Identical same antenna?

[William Sommerwerck]

Nothing is perfectly stable.

This reversal is likely due to a temperature change.

[Mark D. Zacharias[_2_]]

"EADGBE" wrote in message
...

OK...so...this is weird...

I haven't been listening to my SA-400 for a few days, because I just
wasn't that enthused about listening to my garage sale find when I
know that it isn't performing right.

ANYWAY...So I decide to listen to it today while I'm doing some
cleaning up.

I switch it on, and lo and behold, the FM Stereo indicator is back on,
and I verified that it is indeed putting out FM stereo again!

What gives?

In addition to the VCO, the discriminator adjustment may be marginal. Also,
I've seen on some old Technics units that the mono/stereo switch may be
scratchy; also the am/fm band switch.

Mark Z.

[Mike Rivers]

On Dec 3, 12:14 am, EADGBE wrote:

ANYWAY...So I decide to listen to it today while I'm doing some
cleaning up.

I switch it on, and lo and behold, the FM Stereo indicator is back on,
and I verified that it is indeed putting out FM stereo again!

You don't have an antenna connected? Or you have an inadequate
antenna? Unless I use an outdoor antenna, I don't get the stereo pilot
detected on FM radios in my house.

[Arfa Daily]

"Arfa Daily" wrote in message
...

"EADGBE" wrote in message
...

OK...so...this is weird...

I haven't been listening to my SA-400 for a few days, because I just
wasn't that enthused about listening to my garage sale find when I
know that it isn't performing right.

ANYWAY...So I decide to listen to it today while I'm doing some
cleaning up.

I switch it on, and lo and behold, the FM Stereo indicator is back on,
and I verified that it is indeed putting out FM stereo again!

What gives?

Possibly temperature related ? Did you get the reply regarding
discriminator alignment, that I sent you in response to the mail you sent
me direct off-group ?

Arfa


OK I've got the latest mail you have sent me, so I've resent the earlier
reply. Let me know if you don't get it.

Arfa

[Arny Krueger]

"Mike Rivers" wrote in message

On Dec 3, 12:14 am, EADGBE wrote:

ANYWAY...So I decide to listen to it today while I'm
doing some cleaning up.

I switch it on, and lo and behold, the FM Stereo
indicator is back on, and I verified that it is indeed
putting out FM stereo again!

You don't have an antenna connected? Or you have an
inadequate antenna? Unless I use an outdoor antenna, I
don't get the stereo pilot detected on FM radios in my
house.

Sometimes the problem is signal strength, and sometimes the problem is
multipath.

When FM stereo was first introduced, there was some consciousness-raising
about antennas. It seems to have gone away.

[Mr. Land]

On Dec 3, 12:14 am, EADGBE wrote:
OK...so...this is weird...

I haven't been listening to my SA-400 for a few days, because I just
wasn't that enthused about listening to my garage sale find when I
know that it isn't performing right.

ANYWAY...So I decide to listen to it today while I'm doing some
cleaning up.

I switch it on, and lo and behold, the FM Stereo indicator is back on,
and I verified that it is indeed putting out FM stereo again!

What gives?

I've seen stereo multiplex decoder IC's be thermally intermittent in
these
old receivers.

Perhaps try running it with the cover off and (gently) heat up this
section
with a hair dryer. If you can make it fail that way, could be the
problem.

[Mr. Land]

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)

[Arfa Daily]

"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

[Mr. Land]

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.


You're right, I misunderstood your meaning. Sorry.

Definitely agree that the OP should not be attempting to do any IF/Mpx
alignment
w/o proper tools and know-how. I do remember that, even with a test
generator
made expressly for this purpose (which cost about $1000, 20 years
ago), it was
not easy/fun at all.

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 ? :-)


Agree 100%, did not mean to construe otherwise.

Thanks for taking the time to clarify.

[Arfa Daily]

"Mr. Land" wrote in message
...
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.


You're right, I misunderstood your meaning. Sorry.

Definitely agree that the OP should not be attempting to do any IF/Mpx
alignment
w/o proper tools and know-how. I do remember that, even with a test
generator
made expressly for this purpose (which cost about $1000, 20 years
ago), it was
not easy/fun at all.

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 ? :-)


Agree 100%, did not mean to construe otherwise.

Thanks for taking the time to clarify.

No probs

Arfa

[Chuck]

On Sat, 1 Dec 2007 06:30:26 -0800 (PST), EADGBE
wrote:

(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........


I can't remember if this particular model uses a polystyrene 470 or
1000 pf capacitor in the mpx circuit. If it does, I'd replace it with
a polystyrene or silver mica capacitor and readjust the vco. Chuck

[Richard Crowley]

"Chuck" wrote ...
I can't remember if this particular model uses a polystyrene 470 or
1000 pf capacitor in the mpx circuit. If it does, I'd replace it with
a polystyrene or silver mica capacitor and readjust the vco. Chuck

The OP still hasn't answered the obvious question: whether
the 19KHz calibration has slipped again, or whether this is
some other problem.