I'm a electronics tech of sorts.

I just purchased a used Sansui 2000X receiver that has a
noise problem. I got a copy of the schematics and I
think I've located the general area where it is.

How do audio technicians generally go about fixing these things. Do
they
probe with a scope, looking for noise? (I think the problem is
in the ps). Do they have a audio "monitor" that they can
listen to signals at points along the way?

And do you need some special kind of shielded meter probe to
control stray signals from popping high gain circuits?

Just some intro tips would help. I looked around for the 101 stuff
but they are all intros to electronics.

Thanks

I would use an oscilloscope and a 10:1 probe. There won't be enough stray
pickup transmitted into the circuit from the probe to cause problems.

mc wrote:
I would use an oscilloscope and a 10:1 probe. There won't be enough stray
pickup transmitted into the circuit from the probe to cause problems.


Signal tracer (can be as simple as an amplified computer speaker with
improvised probe) is handy....

jak

For troubleshooting, I use a scope, and an audio generator. In your
case, you can terminate the input, open the volume control, and scope
it through to find the stage that is making the noise.

Where troubleshooting for noise can get a bit complicated, is when
there are feedback circuits, thus causing signals to feedback on
themselves.


Jerry G.
======

hfs2 wrote ...
I'm a electronics tech of sorts.

I just purchased a used Sansui 2000X receiver that has a
noise problem. I got a copy of the schematics and I
think I've located the general area where it is.

How do audio technicians generally go about fixing
these things. Do they probe with a scope, looking for
noise? (I think the problem is in the ps).

Can you describe the "noise"? If it is mains-frequency hum
(50Hz or 60Hz depending on where you are) then it is quite
possibly a power supply problem (but not guaranteed).

If it is any other kind of noise (hiss, crackling, etc.)
then the power supply is pretty much free of implication.

Much can be done by just listening and injecting audio
at various points, etc.

Do they have a audio "monitor" that they can
listen to signals at points along the way?

There are "signal tracers" which are essentially an
external amplifier and speaker connected to a probe.
But since this is already an amplifier, you should be
able to work backwards from the speaker and find
where the noise is happening, even without any
external test equipment.

And do you need some special kind of shielded
meter probe to control stray signals from popping
high gain circuits?

10x high-impedance (1M, 10M) probes are frequently
used when probing sensitive circuits. But even those
won't protect you from transients in a high-gain and
high-power audio amplifier. Must follow the schematic
carefuly and probe inteligently.

Just some intro tips would help. I looked around for
the 101 stuff but they are all intros to electronics.

I would work backwards from the output (speaker
amp?) and interrupt/short the signal at each stage to
find where the noise is getting into the signal path.
Don't really need test equipment for that. Of course,
shorting a point where DC is required to maintain
bias (etc.) will cause it to blow up in your face.

And, of course, the usual safety precautions always
apply. Not recommended to proceed if you don't
know what those are.

Thanks for an offer for a preliminary. I don't have any of these
tools, just a
Radioshack $15 meter :-(

Reguardless of input selected (tape, tuner ...) and with the volumn at
zero,
there is hum from both speakers. The hum/noise increases with time as
the reciever warms.

At zero volumn, balance has no effect, nor does anything save the
treble, which
can 'brighten' the high frq component of the hum/noise... just a bit
(treble
control is on the "2nd" preamp board)

There is no noise at the tape out. Tapes record perfectly. (So the
"first" preamp
board must be ok... which leads me to believe the lower voltage ps is
good, the
only ps connected to it.) (However, the 2nd preamp board also takes
power
only from this low voltage powersupply and the treble control, which
effects
the noise a small bit, resides here.)

If I check the signal a the preamp tap (in/out on the back of the
reciever)
and find it good then my plan is to
spend $5 and replace all the ps caps on high voltage ps board.
If that doesn't work, then anther $5 to replace them on the low voltage
supply.

Thanks

If you are just getting hum with nothing connected to the amplifier,
this may be an indication of the power supply filter capacitors going
defective.

--

Jerry G.


wrote in message
oups.com...
Thanks for an offer for a preliminary. I don't have any of these
tools, just a
Radioshack $15 meter :-(

Reguardless of input selected (tape, tuner ...) and with the volumn at
zero,
there is hum from both speakers. The hum/noise increases with time as
the reciever warms.

At zero volumn, balance has no effect, nor does anything save the
treble, which
can 'brighten' the high frq component of the hum/noise... just a bit
(treble
control is on the "2nd" preamp board)

There is no noise at the tape out. Tapes record perfectly. (So the
"first" preamp
board must be ok... which leads me to believe the lower voltage ps is
good, the
only ps connected to it.) (However, the 2nd preamp board also takes
power
only from this low voltage powersupply and the treble control, which
effects
the noise a small bit, resides here.)

If I check the signal a the preamp tap (in/out on the back of the
reciever)
and find it good then my plan is to
spend $5 and replace all the ps caps on high voltage ps board.
If that doesn't work, then anther $5 to replace them on the low voltage
supply.

Thanks

wrote in message
oups.com
I'm a electronics tech of sorts.

I just purchased a used Sansui 2000X receiver that has a
noise problem. I got a copy of the schematics and I
think I've located the general area where it is.

How do audio technicians generally go about fixing these
things.

http://www.repairfaq.org/sam/tshoot.htm

wrote ...
If I check the signal a the preamp tap (in/out on the back of the
reciever)
and find it good then my plan is to
spend $5 and replace all the ps caps on high voltage ps board.
If that doesn't work, then anther $5 to replace them on the low
voltage
supply.

The symptoms make it sound like the main PS filter caps
have dried out. But I'd bet that your $5 estimate is way too
low for such big capacitors.