Pioneer sx-727 FM problem

T

tony

Guest
Hi,
I have a Pioneer sx-727. I'm the original owner over 40 years.
Recently developed fm problem.
Loud crackling sound on fm station and then station drifts. No noise
at all between stations.
AM reception also not good, background buzz, humm between
stations on AM only. Unit works perfectly with CD and other inputs.
Any ideas what my problem might be? This all started a couple of weeks
ago,
when I noticed that signal strength meter was not illuminated, I
assumed just bulb burned out.
Tuning center meter still works. Any help would be appreciated.
Thanks.
 
"Jeff Urban" <jurb6006@gmail.com> wrote in message
news:eac31162-9ea1-4f4c-a1db-47c4f8484bc4@sk8g2000pbc.googlegroups.com...

If there's no noise between stations with the muting off it's probably
oscillating. That would maybe indicate filters or bypass caps. If the
frequency actually drifts, assuming it has ONE fault which is usual,
look around the FM oscillator or mixer stages.
Click to expand...
What about a dead LO or mixer?

If you have a 100MHz 'scope, you should be able to trace through the front
end and IF.
 
If there's no noise between stations with the muting off it's probably
oscillating. That would maybe indicate filters or bypass caps. If the
frequency actually drifts, assuming it has ONE fault which is usual,
look around the FM oscillator or mixer stages.

I think buzz between AM stations is just about normal these days,
unless you specifically noticed a difference at the same time the FM
fault showed up.

Actually RF is not really my strong suit, but it's still electronics.
If that reciever uses discrete transistors for the FM, it might be a
bit hard to find someone who really remembers how to work on it. That
reciever is old enough for a pension, but by all means try to keep it
alive.

J
 
On Feb 10, 1:52 pm, Jeff Urban <jurb6...@gmail.com> wrote:
If there's no noise between stations with the muting off it's probably
oscillating. That would maybe indicate filters or bypass caps. If the
frequency actually drifts, assuming it has ONE fault which is usual,
look around theFMoscillator or mixer stages.

I think buzz between AM stations is just about normal these days,
unless you specifically noticed a difference at the same time theFM
fault showed up.

Actually RF is not really my strong suit, but it's still electronics.
If that reciever uses discrete transistors for theFM, it might be a
bit hard to find someone who really remembers how to work on it. That
reciever is old enough for a pension, but by all means try to keep it
alive.

J
Click to expand...
Thanks for the info.
I looked at the AWR-011, Power supply unit board.
Anyone know what the tolerance should be on these voltages.
For the AWR-011, Power Supply unit board
the schematic says
pin 2,5,6,7 12.5v, 30v, 30v, 36v
I'm measuring
pin 2,5,6,7 10.5v, 27.5v, 27.5v, 33v

Is this within tolerance?

Also anyone know what the output of the big transformer
(ATT-050)should be
Nothing listed on the schematics.
I'm measuring
pins 13, 12, 10, 3 26vAC, 25.5vAC, 35v AC, 0 (AWR-011 board).

Thanks.
 
On Feb 10, 1:52 pm, Jeff Urban <jurb6...@gmail.com> wrote:
If there's no noise between stations with the muting off it's probably
oscillating. That would maybe indicate filters or bypass caps. If the
frequency actually drifts, assuming it has ONE fault which is usual,
look around theFMoscillator or mixer stages.

I think buzz between AM stations is just about normal these days,
unless you specifically noticed a difference at the same time theFM
fault showed up.

Actually RF is not really my strong suit, but it's still electronics.
If that reciever uses discrete transistors for theFM, it might be a
bit hard to find someone who really remembers how to work on it. That
reciever is old enough for a pension, but by all means try to keep it
alive.

J
Click to expand...
Thanks for the info.
Anyone know what the tolerance should be on these voltages.
For the AWR-011, Power Supply unit board
the schematic says
pin 2,5,6,7 12.5v, 30v, 30v, 36v
I'm measuring
pin 2,5,6,7 10.5v, 27.5v, 27.5v, 33v

Is this within tolerance?

Also anyone know what the output of the big transformer
(ATT-050)should be
Nothing listed on the schematics.
I'm measuring
pins 13, 12, 10, 3 26vAC, 25.5vAC, 35v AC, 0 (AWR-011 board).
 
tony wrote:
Hi,
I have a Pioneer sx-727. I'm the original owner over 40 years.
Recently developed fm problem.
Loud crackling sound on fm station and then station drifts. No noise
at all between stations.
AM reception also not good, background buzz, humm between
stations on AM only. Unit works perfectly with CD and other inputs.
Any ideas what my problem might be? This all started a couple of weeks
ago,
when I noticed that signal strength meter was not illuminated, I
assumed just bulb burned out.
Tuning center meter still works. Any help would be appreciated.
Thanks.
Click to expand...
Hi Tony,

If you can hear the stations at all and they're randomly drifting try
squirting some tuner shower/contact cleaner into the tuning gang where the
rotating shaft contacts the bearings. There should be two or three bearings.
Then, move the tuning dial quickly from 88 to 108 back and forth several
times. You might have to spray several times to get the most benefit from
the cleaning. Did that help?

--
David Farber
Los Osos, CA
 
On 2/10/2012 8:15 AM, tony wrote:
Hi,
I have a Pioneer sx-727. I'm the original owner over 40 years.
Recently developed fm problem.
Loud crackling sound on fm station and then station drifts. No noise
at all between stations.
AM reception also not good, background buzz, humm between
stations on AM only. Unit works perfectly with CD and other inputs.
Any ideas what my problem might be? This all started a couple of weeks
ago,
when I noticed that signal strength meter was not illuminated, I
assumed just bulb burned out.
Tuning center meter still works. Any help would be appreciated.
Thanks.
Click to expand...
Tony,

Have a look at the soldering on the regulator transistors on the power
supply board, and elsewhere. While its been a while since I've seen one
of these, I remember soldering on the pass transistors getting really
awful. Look for overheated, crystallized looking connections. if you
find some, desolder and re-solder them.

Regards,
Tim Schwartz
Bristol Electronics
 
On Feb 13, 5:30 pm, Tim Schwartz <t...@bristolnj.com> wrote:
On 2/10/2012 8:15 AM, tony wrote:

Hi,
I have a Pioneersx-727. I'm the original owner over 40 years.
Recently developedfmproblem.
Loud crackling sound onfmstation and then station drifts. No noise
at all between stations.
AM reception also not good, background buzz, humm between
stations on AM only. Unit works perfectly with CD and other inputs.
Any ideas what myproblemmight be? This all started a couple of weeks
ago,
when I noticed that signal strength meter was not illuminated, I
assumed just bulb burned out.
Tuning center meter still works. Any help would be appreciated.
Thanks.

Tony,

        Have a look at the soldering on the regulator transistors on the power
supply board, and elsewhere.  While its been a while since I've seen one
of these, I remember soldering on the pass transistors getting really
awful.  Look for overheated, crystallized looking connections.  if you
find some, desolder and re-solder them.

Regards,
Tim Schwartz
Bristol Electronics
Click to expand...
Thanks for the info. I'll look at soldering on the regulators.
The outputs on the power supply board are withing spec but on the low
side.
AWR-011,
the schematic says
pin 2,5,6,7 12.5v, 30v, 30v, 36v
I'm measuring
pin 2,5,6,7 10.5v, 27.5v, 27.5v, 33v

However the collector of Q3 schematic says 36v, I measure ~20v.
I'm not sure if that's a problem. This is on the power supply board
AWR-011.
Thanks.
 
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