I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

Any help would be much appreciated.

EADGBE wrote:
I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

Your notion of "halfway" is sort of optimistic.

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

Odds are the stereo detector stage needs alignment or else it has some
other issue with it. Take it to a tech. The audio output of the
FM detector goes through a coupling cap into a second discriminator
stage. All kinds of things can go wrong with it.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

No, the stereo demodulation circuit is bad.

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

If you have a 300 ohm source, you use the 300 ohm input. If you have
a 75 ohm source, you use the 75 ohm input. Usually there is a balun
inside the case which transforms one to the other, and the balun is
a little lossy, so one of the inputs will have slightly better sensitivity.
Which is basically academic since you will need the correct one for your
source anyway.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message
...
EADGBE wrote:
I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

Your notion of "halfway" is sort of optimistic.

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

Odds are the stereo detector stage needs alignment or else it has some
other issue with it. Take it to a tech. The audio output of the
FM detector goes through a coupling cap into a second discriminator
stage. All kinds of things can go wrong with it.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

No, the stereo demodulation circuit is bad.

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

If you have a 300 ohm source, you use the 300 ohm input. If you have
a 75 ohm source, you use the 75 ohm input. Usually there is a balun
inside the case which transforms one to the other, and the balun is
a little lossy, so one of the inputs will have slightly better
sensitivity.
Which is basically academic since you will need the correct one for your
source anyway.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

To add to Scott's reply:- The 300 ohm input will be balanced twin feeder.
This is the cable with two parallel wires, spaced about 12mm (1/2") apart.
The 75 ohm input is unbalanced and uses coaxial (screened) cable. In the UK,
we prefer to use the 75 ohm input as screened cable protects the antenna
signal from interference, especially from mains wiring and/or metal objects
which could change the impedance of the balanced unscreened cable.

Having said that, Scott is right in that if you have a 75 ohm antenna, use
coax, if you have a 300 ohm antenna use balanced twin.

S.



--
http://audiopages.googlepages.com

EADGBE wrote:
I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

The SA designation is still used for their receiver line, and has been
since Matsu****a formed the Technics brand. How old is it?

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

Depends very strongly on where you are, geographically speaking...and
where the receiver is physically located.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Those work acceptably in urban settings. If it's hooked up right, and
there are reasonably strong stations within 15-30 miles, you should get
stereo.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

Depends. Obviously if the gear is old, it could be defective.

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

It's not resistance, but impedance...probably beyond a concise
explanation. Suffice to say: hook twinlead (what you have) to the 300
ohm connection and coax (like cable TV lead) otherwise.

jak

Any help would be much appreciated.

Scott:

I am fully aware of the Technics' questionable "hi-fi" status. I
simply bought this as a nostalgia trip. Believe me, the Technics SA
receiver I had as a kid was AUDIOPHILE stuff compared to what I had
been listening to before I got it.

For the record, the receiver I just got is an SA-400, made from 1978
to 1979.

On Nov 6, 2:07 pm, EADGBE wrote:
Scott:

I am fully aware of the Technics' questionable "hi-fi" status. I
simply bought this as a nostalgia trip. Believe me, the Technics SA
receiver I had as a kid was AUDIOPHILE stuff compared to what I had
been listening to before I got it.

For the record, the receiver I just got is an SA-400, made from 1978
to 1979.

Stereo notwithstanding, can you get decent sensitivity at both ends of
the
FM band?

I used to work on a lot of these types of receivers. Our shop's
standard
"tune-up" for these included FM sensitivity adjustments (i.e. RF
alignment)
at several points along the FM band, and IF and stereo demux
alignment.
For the RF alignment, you could probably approximate the optimal
tuning
if you can find relatively weak stations at both ends of the band.

For the IF and stereo demux, though, we used a combination of a
dedicated signal generator and a 'scope. Not sure if or how you could
accomplish that w/o some specialized test equipment.

I was always a little surprised at how far off these old technology
receivers could be, even when they weren't that old.

If you're getting decent signal meter deflection, I agree with the
other
poster(s) - you probably need your IF/Stereo demux aligned.

Good Luck!

EeAaDdGgBbEe (a 12-string)

EADGBE wrote:
Scott:

I am fully aware of the Technics' questionable "hi-fi" status. I
simply bought this as a nostalgia trip. Believe me, the Technics SA
receiver I had as a kid was AUDIOPHILE stuff compared to what I had
been listening to before I got it.

For the record, the receiver I just got is an SA-400, made from 1978
to 1979.


You probably have this info, but: 45wpc at 0.04 THD and 0.04 IMD rated
from 20-20khz bandwidth with a 90 dB s/n ratio (phono). 10.8 fm mono IHF
sensitivity with a 1.2 dB fm capture ratio...cost $360 in 1979 dollars
(over $1000 today, by the consumer price index).

By some measures, I'd day that qualified as "HiFi".


jak

On Nov 6, 1:20 pm, EADGBE wrote:
I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

Any help would be much appreciated.

see if you can locate a schematic or serivce manual and look for a
muting or stereo threshold adjustment...

these receivers are designed to switch to mono when the signal is weak
and sometimes there is an adjustment for the threshold...

or the tuner could be out of alignment or broke such that it thinks
the signal is weak when its not weak...

Mark

"EADGBE" wrote in message
oups.com...

Scott:

I am fully aware of the Technics' questionable "hi-fi" status. I
simply bought this as a nostalgia trip. Believe me, the Technics SA
receiver I had as a kid was AUDIOPHILE stuff compared to what I had
been listening to before I got it.

For the record, the receiver I just got is an SA-400, made from 1978
to 1979.


VR301 is the VCO adjustment. It's located near the tuning gang. This would
be the easiest thing to adjust that might correct the problem. First take
note of where it's set so that if the adjustment doesn't work, you can
return it to its prior state. Then turn it slightly one way or the other and
see if your stereo signal light comes on for more stations. If not, go the
other direction. Without a frequency counter, you'll need to trial and error
this adjustment.

Good luck.

--
David Farber
David Farber's Service Center
L.A., CA

In article , Meat Plow wrote:
On Tue, 06 Nov 2007 10:20:48 -0800, EADGBE wrote:

I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

Need to align the stereo section of the tuner which requires some
equipment that generates specific signals.

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

75 ohm is coax type connection, 300 ohm is twin lead. The often have a
common input terminal.

75 is commonly unbalanced, or uses ground reference. I do have some 72 ohm
balanced lead next to me, and there is no shield. You can buy balanced
shielded however. I used to use some 300 ohm shielded lead for a TV antenna
way back. One of my tuners I started to use, which I bought of Ebay, is slightly off
tune, and you have to hit mono to get good reception. It can also affect the stereo
and muting thresholds.

greg

"David Farber" wrote in message
...

VR301 is the VCO adjustment. It's located near the tuning gang. This would
be the easiest thing to adjust that might correct the problem. First take
note of where it's set so that if the adjustment doesn't work, you can
return it to its prior state. Then turn it slightly one way or the other
and
see if your stereo signal light comes on for more stations. If not, go the
other direction. Without a frequency counter, you'll need to trial and
error
this adjustment.

It's highly likely this is the problem. This setting can drift to the point
where the decoder can fail to switch to stereo. I've seen the same issue in
other stereo receivers.

On Nov 6, 2:33 pm, "Mr. Land" wrote:

Stereo notwithstanding, can you get decent sensitivity at both ends of
the
FM band?

Oh, yes. In fact, the tuner pulls in most stations quite clearly even
when there is NO antenna connected at all.

With an antenna, the signal strength meter and FM fine-tuning meter
both respond VERY strongly, throughout the entire FM band.

The signal strength meter typically registers between 3.5 and 4.5, on
a scale of 1 to 5, and the fine-tuning meter always allows me to
precisely "center" the tuning onto a station.


EeAaDdGgBbEe (a 12-string)


LOL!!! Good to see a fellow guitar player who understands my
"name"!!!

On Nov 6, 3:53 pm, "David Farber" wrote:

VR301 is the VCO adjustment. It's located near the tuning gang. This would
be the easiest thing to adjust that might correct the problem. First take
note of where it's set so that if the adjustment doesn't work, you can
return it to its prior state. Then turn it slightly one way or the other and
see if your stereo signal light comes on for more stations. If not, go the
other direction. Without a frequency counter, you'll need to trial and error
this adjustment.


David:

Thanks so much for the information. I work on analog stuff (tape
decks, turntables), but I'm not too well-versed in tuner circuitry.
This will be a big help.

FWIW, I do have a frequency counter, but it's not in hand just yet.
(Just ordered it.)

"EADGBE" wrote in message
oups.com...
I went to a garage sale recently and couldn't pass up an old Technics
SA series receiver in great condition. (A Technics SA series receiver
was my first bit of halfway decent stereo equipment.)

The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.

I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Could something be weak in the FM tuner circuitry, or do I need a
stronger antenna?

And whilst I'm at it, what is the functional difference between the
two 300 ohm FM antenna terminals and the grounded 75 ohm FM antenna
terminal, besides the obvious difference in resistance?

Any help would be much appreciated.


It's the VCO adjustment...

Mark Z.

In article ,
jakdedert wrote:
I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Those work acceptably in urban settings. If it's hooked up right, and
there are reasonably strong stations within 15-30 miles, you should get
stereo.

The problem with these in an urban area is they do little to sort
multipath problems - which are all too common with high buildings etc
around. And multipath can cause very audible distortion.

--
*Virtual reality is its own reward*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
jakdedert wrote:
I only have one of those little clear-coated two-conductor wire FM
antennas hooked up to it right now, but if I recall correctly, that
was all that was needed to get FM Stereo on virtually every station in
my area.

Those work acceptably in urban settings. If it's hooked up right, and
there are reasonably strong stations within 15-30 miles, you should get
stereo.

The problem with these in an urban area is they do little to sort
multipath problems - which are all too common with high buildings etc
around. And multipath can cause very audible distortion.

True, but irrelevant to the OP's issue.

jak

OK, I accessed VR301 - plainly labeled "VCO" by the way - and turned
it clockwise a very tiny amount.

That did the trick!

I now have FM Stereo indication on all stations!

Thanks so much to David, William, Mark, and everyone else who offered
information/suggestions.

My garage sale find is now 100% functional!

"EADGBE" wrote in message
oups.com...
On Nov 6, 3:53 pm, "David Farber" wrote:

VR301 is the VCO adjustment. It's located near the tuning gang. This
would
be the easiest thing to adjust that might correct the problem. First
take
note of where it's set so that if the adjustment doesn't work, you can
return it to its prior state. Then turn it slightly one way or the other
and
see if your stereo signal light comes on for more stations. If not, go
the
other direction. Without a frequency counter, you'll need to trial and
error
this adjustment.


David:

Thanks so much for the information. I work on analog stuff (tape
decks, turntables), but I'm not too well-versed in tuner circuitry.
This will be a big help.

FWIW, I do have a frequency counter, but it's not in hand just yet.
(Just ordered it.)



I looked at the service manual again and the alternative method of alignment
says to adjust VR301 until the stereo light comes on. When you get your
counter, hook it up to TP301 via 100k ohm resistor and adjust VR301 for
19KHz. It might help if you move the tuning dial so there is no station
being received during the test.
--
David Farber
David Farber's Service Center
L.A., CA

Serge Auckland wrote:


The receiver's FM tuner works great and sounds very good, but I can
only get the "FM Stereo" indicator light to light up on one station,
even though the signal strength meter indicates VERY strong FM signals
on almost every station all across the FM band.


But .. is the output stereo? The indicator could be bad ... it is
on my old (and very excellent) Sony tuner.

This is supposedly a pro group. Record the output and look at the
waveforms in your favorite editor. Are they completely different?
Are there places where they are 90 degrees out of phase? Then
it is working OK in stereo on that station. Or just listen!


Doug McDonald