quartz lock tuner problem

[Dave]

I recently purchased a Sansui T-80 digitally quart-locked tuner. This guy
has both an analog tuning scale and a digital frequency readout. It's also
got a tuning meter which tells you which way to turn the knob for perfect
tuning (looks like --> o <-- ). When you hit the center of the signal, the
quartz-lock indicator lights up and all is good. For awhile. After 15-30
minutes, the quartz-lock is lost. The muting kicks in and the audio signal
cuts in and out. The tuning indicator always indicates that downward tuning
is required; when you tune down, the quartz lock light comes on for a second
or so and you get sound, then the tuning indicator says "down" again. This
repeats until the digital frequency drops by 0.1MHz, at which point, the
"up" indicator lights up. It's a viscious circle.

Now, this tuner has a combined muting/stereo button so that when muting is
off the unit goes to mono. When in mono, no problem. Quartz-lock light
stays on, tuning indicator stays centered. When the problem occurs and I
switch to mono, whatever warm component is causing the problem cools off
because after a few minutes I can go back to stereo for another 15-30
minutes of trouble-free operation. I am thinking there may be a bad cap in
the stereo circuit?

I've ordered a service manual with schematic. Can anyone tell me what
problems might cause a quartz-locked tuner to drift? I popped the top panel
off thinking if there are only a few electrolytic caps I'd replace them all
given that this tuner is probably 20 years old. There are over forty of
varying sizes on several boards.

Any help greatly appreciated.

Dave

[Codifus]

Post by Dave
I recently purchased a Sansui T-80 digitally quart-locked tuner. This guy
has both an analog tuning scale and a digital frequency readout. It's also
got a tuning meter which tells you which way to turn the knob for perfect
tuning (looks like --> o <-- ). When you hit the center of the signal, the
quartz-lock indicator lights up and all is good. For awhile. After 15-30
minutes, the quartz-lock is lost. The muting kicks in and the audio signal
cuts in and out. The tuning indicator always indicates that downward tuning
is required; when you tune down, the quartz lock light comes on for a second
or so and you get sound, then the tuning indicator says "down" again. This
repeats until the digital frequency drops by 0.1MHz, at which point, the
"up" indicator lights up. It's a viscious circle.
Now, this tuner has a combined muting/stereo button so that when muting is
off the unit goes to mono. When in mono, no problem. Quartz-lock light
stays on, tuning indicator stays centered. When the problem occurs and I
switch to mono, whatever warm component is causing the problem cools off
because after a few minutes I can go back to stereo for another 15-30
minutes of trouble-free operation. I am thinking there may be a bad cap in
the stereo circuit?
I've ordered a service manual with schematic. Can anyone tell me what
problems might cause a quartz-locked tuner to drift? I popped the top panel
off thinking if there are only a few electrolytic caps I'd replace them all
given that this tuner is probably 20 years old. There are over forty of
varying sizes on several boards.
Any help greatly appreciated.
Dave

Try these guys;

fmtunerinfo.com

CD

[JANA]

Most likely some component changing value in the front end, or the AFC, or
the AGC area. You would have to give out the tuner to someone who has the
proper set-up, is experienced in troubleshooting these types of faults, and
has the calibration equipment to get things adjusted after the parts are
replaced.
--
JANA
_____


"Dave" <***@yahoo.delete.com> wrote in message news:m82ef.196635$***@edtnps90...
I recently purchased a Sansui T-80 digitally quart-locked tuner. This guy
has both an analog tuning scale and a digital frequency readout. It's also
got a tuning meter which tells you which way to turn the knob for perfect
tuning (looks like --> o <-- ). When you hit the center of the signal, the
quartz-lock indicator lights up and all is good. For awhile. After 15-30
minutes, the quartz-lock is lost. The muting kicks in and the audio signal
cuts in and out. The tuning indicator always indicates that downward tuning
is required; when you tune down, the quartz lock light comes on for a second
or so and you get sound, then the tuning indicator says "down" again. This
repeats until the digital frequency drops by 0.1MHz, at which point, the
"up" indicator lights up. It's a viscious circle.

Now, this tuner has a combined muting/stereo button so that when muting is
off the unit goes to mono. When in mono, no problem. Quartz-lock light
stays on, tuning indicator stays centered. When the problem occurs and I
switch to mono, whatever warm component is causing the problem cools off
because after a few minutes I can go back to stereo for another 15-30
minutes of trouble-free operation. I am thinking there may be a bad cap in
the stereo circuit?

I've ordered a service manual with schematic. Can anyone tell me what
problems might cause a quartz-locked tuner to drift? I popped the top panel
off thinking if there are only a few electrolytic caps I'd replace them all
given that this tuner is probably 20 years old. There are over forty of
varying sizes on several boards.

Any help greatly appreciated.

Dave

[Tim Schwartz]

Dave,

It could be something as simple as a bad trim pot internally, which
could cause an oscillator to be off frequency. Wait until you get the
manual and check the multiplex alignment. While monitoring the
frequency (usually 76Khz), tap on the adjustment pot and see if it
drifts all over the place. You might simply need to move the trip pots
back and forth to clean them, but be sure you can put them back EXACTLY
where they were, or just do a full alignment and see where that gets
you. I'd leave it alone until you've got the manual.

Regards,
Tim Schwartz
Bristol Electronics

Post by Dave
I recently purchased a Sansui T-80 digitally quart-locked tuner. This guy
has both an analog tuning scale and a digital frequency readout. It's also
got a tuning meter which tells you which way to turn the knob for perfect
tuning (looks like --> o <-- ). When you hit the center of the signal, the
quartz-lock indicator lights up and all is good. For awhile. After 15-30
minutes, the quartz-lock is lost. The muting kicks in and the audio signal
cuts in and out. The tuning indicator always indicates that downward tuning
is required; when you tune down, the quartz lock light comes on for a second
or so and you get sound, then the tuning indicator says "down" again. This
repeats until the digital frequency drops by 0.1MHz, at which point, the
"up" indicator lights up. It's a viscious circle.
Now, this tuner has a combined muting/stereo button so that when muting is
off the unit goes to mono. When in mono, no problem. Quartz-lock light
stays on, tuning indicator stays centered. When the problem occurs and I
switch to mono, whatever warm component is causing the problem cools off
because after a few minutes I can go back to stereo for another 15-30
minutes of trouble-free operation. I am thinking there may be a bad cap in
the stereo circuit?
I've ordered a service manual with schematic. Can anyone tell me what
problems might cause a quartz-locked tuner to drift? I popped the top panel
off thinking if there are only a few electrolytic caps I'd replace them all
given that this tuner is probably 20 years old. There are over forty of
varying sizes on several boards.
Any help greatly appreciated.
Dave

[Dave]

Post by Tim Schwartz
Dave,
It could be something as simple as a bad trim pot internally, which
could cause an oscillator to be off frequency. Wait until you get the
manual and check the multiplex alignment. While monitoring the
frequency (usually 76Khz), tap on the adjustment pot and see if it
drifts all over the place. You might simply need to move the trip pots
back and forth to clean them, but be sure you can put them back EXACTLY
where they were, or just do a full alignment and see where that gets
you. I'd leave it alone until you've got the manual.

Thanks for your reply, Tim.

If it was a bad trim pot, why would the condition only occur when the
stereo/muting is switched off. As I noted, it will be stable all day long
in mono mode. Switch to stereo and the clock starts ticking...

???

Dave

[Barry Mann]

Post by Dave

Post by Tim Schwartz
Dave,
It could be something as simple as a bad trim pot internally, which
could cause an oscillator to be off frequency. Wait until you get the
manual and check the multiplex alignment. While monitoring the
frequency (usually 76Khz), tap on the adjustment pot and see if it
drifts all over the place. You might simply need to move the trip pots
back and forth to clean them, but be sure you can put them back EXACTLY
where they were, or just do a full alignment and see where that gets
you. I'd leave it alone until you've got the manual.

Thanks for your reply, Tim.
If it was a bad trim pot, why would the condition only occur when the
stereo/muting is switched off. As I noted, it will be stable all day
long in mono mode. Switch to stereo and the clock starts ticking...

I think there is a problem with the alignment and/or the AFC. It is
very common to switch off the AFC, stereo, and muting at the same time.

Once the AFC is switched off, the tuner will not attempt to sit on the
center of the channel. For a properly aligned tuner the detector DC
voltage should be zero when tuned to the center of the channel. Any non
zero component will be feed to the local oscillator as a correction.

If there is a DC offset associated with the AFC, the tuner will tend to
move away from the center. This can be complicated by a touch sensitive
tuning knob that will disable the AFC during tuning. There is usually a
delay associated with the touch circuit releasing the AFC. If the
timing capacitor is leaking, it could take a while to release, thus
delaying the problematic AFC from moving the tuning point.

-----------------------------------------------------------
spam: ***@ftc.gov
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

[Dave]

Post by Barry Mann
I think there is a problem with the alignment and/or the AFC. It is
very common to switch off the AFC, stereo, and muting at the same time.
Once the AFC is switched off, the tuner will not attempt to sit on the
center of the channel. For a properly aligned tuner the detector DC
voltage should be zero when tuned to the center of the channel. Any non
zero component will be feed to the local oscillator as a correction.
If there is a DC offset associated with the AFC, the tuner will tend to
move away from the center. This can be complicated by a touch sensitive
tuning knob that will disable the AFC during tuning. There is usually a
delay associated with the touch circuit releasing the AFC. If the
timing capacitor is leaking, it could take a while to release, thus
delaying the problematic AFC from moving the tuning point.

I will start by replacing all of the electrolytics in the AFC circuit, then
work on alignment. If one capcitor is leaking however slightly across the
terminals, that could inject a DC voltage into the tuning circuit. As I
noted in my original post it only drifts DOWN, never up. This would tend to
indicate to me that the voltage polarity causing the drift is constant which
would be consistent with a leaking or shorted capacitor. Only leaks/shorts
when at operating temp so it would work fine for awhile. No?

Thanks for your help.

Dave

Post by Barry Mann
-----------------------------------------------------------
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

[Barry Mann]

Post by Dave
I recently purchased a Sansui T-80 digitally quart-locked tuner. This
guy has both an analog tuning scale and a digital frequency readout.
It's also got a tuning meter which tells you which way to turn the
knob for perfect tuning (looks like --> o <-- ). When you hit the
center of the signal, the quartz-lock indicator lights up and all is
good. For awhile. After 15-30 minutes, the quartz-lock is lost. The
muting kicks in and the audio signal cuts in and out. The tuning
indicator always indicates that downward tuning is required; when you
tune down, the quartz lock light comes on for a second or so and you
get sound, then the tuning indicator says "down" again. This repeats
until the digital frequency drops by 0.1MHz, at which point, the "up"
indicator lights up. It's a viscious circle.
Now, this tuner has a combined muting/stereo button so that when
muting is off the unit goes to mono. When in mono, no problem.
Quartz-lock light stays on, tuning indicator stays centered. When the
problem occurs and I switch to mono, whatever warm component is
causing the problem cools off because after a few minutes I can go
back to stereo for another 15-30 minutes of trouble-free operation. I
am thinking there may be a bad cap in the stereo circuit?
I've ordered a service manual with schematic. Can anyone tell me what
problems might cause a quartz-locked tuner to drift? I popped the top
panel off thinking if there are only a few electrolytic caps I'd
replace them all given that this tuner is probably 20 years old.
There are over forty of varying sizes on several boards.
Dave

Check the discriminator balance -- generally the tuning lights should
balance when you are tuned in a blank spot.

Also check the supply voltage, it may be a bit low. Check to see that
it is steady.

Note that the AFC and muting are often turned off when the unit is
forced into MONO. Sometimes the AFC is turned off when you touch the
tuning knob.

If the unit is out of alignment, the AFC can work against you.
Eventually, the AFC drives the tuner so far off station that the muting
circuit shuts off the output. At that point you grab the knob and make
a correction (adjusting the situation to a slightly different point).

Does this unit claim "quartz lock"? From your description it seems like
a regular old analog tuner with a frequency counter on the side. A true
synthesized tuner would not have a standard pointer dial, only the
display.

---

You can fuss with the unit if you like, but proper instrumentation
makes the job much easier. (as does experience with a few hundred
tuners)

-----------------------------------------------------------
spam: ***@ftc.gov
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

[s***@pitt.edu]

Post by Dave
I recently purchased a Sansui T-80 digitally quart-locked tuner. This guy
has both an analog tuning scale and a digital frequency readout. It's also
got a tuning meter which tells you which way to turn the knob for perfect
tuning (looks like --> o <-- ). When you hit the center of the signal, the
quartz-lock indicator lights up and all is good. For awhile. After 15-30
minutes, the quartz-lock is lost. The muting kicks in and the audio signal
cuts in and out. The tuning indicator always indicates that downward tuning
is required; when you tune down, the quartz lock light comes on for a second
or so and you get sound, then the tuning indicator says "down" again. This
repeats until the digital frequency drops by 0.1MHz, at which point, the
"up" indicator lights up. It's a viscious circle.
Now, this tuner has a combined muting/stereo button so that when muting is
off the unit goes to mono. When in mono, no problem. Quartz-lock light
stays on, tuning indicator stays centered. When the problem occurs and I
switch to mono, whatever warm component is causing the problem cools off
because after a few minutes I can go back to stereo for another 15-30
minutes of trouble-free operation. I am thinking there may be a bad cap in
the stereo circuit?
I've ordered a service manual with schematic. Can anyone tell me what
problems might cause a quartz-locked tuner to drift? I popped the top panel
off thinking if there are only a few electrolytic caps I'd replace them all
given that this tuner is probably 20 years old. There are over forty of
varying sizes on several boards.
Any help greatly appreciated.
Dave

My first reaction, touch, feel, get out the bottle of Freezz, and a
heat
gun (hair dryer). Sometimes touching with a soldering iron. Then
experiment.
So If there is a thermal indication, the trouble is most easily
troubleshot
using some of these tools.

greg