[sdiy] Non-DIY, but looking for repair advice...

[Mike Bryant]

First of all measure the voltages on the output op-amp power rails.

If they are reasonable, look at the op-amp itself.  The highly attenuated signal could be it passing from a previous stage through the feedback resistor to the output.  Op-amps reject PSU hum really well, but not when they are dead.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of John Ames via Synth-diy <synth-diy at synth-diy.org>
Sent: 13 May 2024 01:01
To: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: [sdiy] Non-DIY, but looking for repair advice...

Slightly not-strictly-OT here, I s'pose, but I'm looking for hints/
advice - I've got a Yamaha CS-5 that's mostly in good working order, but
has two (possibly related) issues. One is that there's a slight 60 Hz
buzz from the PSU - it's present even with the mixer sources turned
off, but the filter can remove it. The other is that the output is very
weak; running direct into my recording workstation, the maximum
amplitude is lower than -30dB! Of course I could pre-amplify it...but
then that boosts the AC hum from "not really audible" to "far too
noticeable" :/

Now, I haven't had it open yet; before I go poking around willy-nilly I
thought I'd ask for any advice, and raise what may well be an important
point. This is, or was, a Japanese import model, and the print on the
back near the power cord lists it as a 100V device - but somewhere
along the line someone covered that over with masking tape and Sharpied
"115V" on it. I've never had problems running 100V equipment on US line
voltages before, but admittedly it's almost all been digital gear; is
that potentially an issue? And someone might have done a mod to adapt
this thing for that already; any ideas what to look for if I open it up?
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