Long shot: troubleshooting audio amp

[Anthony Olejnik]

Hi,

I've 'been away' from electronics for quite some time.
I have acquired an old (1988) Ensoniq Digital Piano with
built-in (stereo) amps (by Bose).

The stereo amps appear to be two separate mono amp modules
each going to a built-in speaker.

Problem:
One channel/side (the left), which BTW, is nearest to
the AC transformer, is constantly oscillating a variable
high-pitch tone. It is not a 60Hz hum.

I suspect that one of the components (filter cap?) has gone bad.

Q: What are some trouble-shooting steps I could take to:
- determine what is causing the oscillation variable high-
pitch tone
and - to actually fix it.

(NOTE: The right amp module is fine (and appears to be identical).)

Any help would be greatly appreciated.
Many thanks in advance.

--tony

[Uwe Zimmermann]

If the two modules are identical, would it be possible to swap them on
the input side and/or regarding their physical position inside the
instrument. This would help to identify if the problem really is with
the amplifiers, it it's noise pickup from somewhere else or if it's
caused already somewhere in the pre-amp stages.

Uwe.

[to...@nospamprepair.com]

Take a look at the components and see if it utilizes an output module
IC...like a TDA 2040 or an LM3886, etc. If so, my bet is that it's the
IC...it usually is.

to...@amprepair.com

"Anthony Olejnik" <to...@pobox.upenn.edu> wrote in message
news:slrn3vsatcm...@pobox.upenn.edu...

[N. Thornton]

to...@pobox.upenn.edu (Anthony Olejnik) wrote in message news:<slrn3vsatcm...@pobox.upenn.edu>...

Q1: where does the noise originate, amp or signal generation section.
Short the amp's input: does it silence it? That'd be my first move I think.

Regards, NT

[Frontline Electronics]

Bose likes to use Nichicon caps, I do not.
Jeff

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