OK, this is what I found:
I was thinking that it had to be this, that I cut and saved from AH (I think) a few years ago:
"Seems the SH card collects debris over the years from being near the front
of the machine, underneath the keyboard, and this reduces its effectiveness
as an insulator. The impedance of the input to the SH amps (CA3140T) is in
the order of 1.5 T Ohms (1500 Meg Ohms!) and the SH caps are quite small for
this application (0.22uF) so it doesn't take much to cause that voltage to
leak away. Some good old household dust plus several gigs in smokey
theatres (this was the eighties, don't forget) would probably be enough.
I found if I lifted the end of the caps which feed to the CA3140T's from the
PCB, Pin 3 of the CA3140T's and also the 4066 Gate outputs and wire-linked
them together away from the surface of the PCB, the problem goes away. There
is still a very small voltage drop but even with full Sustain (Yamaha-speak
for Release) the change in pitch isn't noticeable.
I'm guessing this must be a common fault, as the CS-60 card I have exhibits
the same problem.
Lucid."
jkjelec
----- Original Message -----
From: "lucidsound" <lucidsound@...>
To: yamahacs80@yahoogroups.com
Sent: Thursday, May 12, 2011 2:33:54 PM
Subject: [yamahacs80] Pitch Drop When Using Sustain 1
Has anyone else come across the quirk whereby if using long release times in Sustain Mode 1, the oscillator pitch drops slowly when the notes are released? Switching to Sustain II brings the notes back to the correct pitch.
I figure this is something to do with the Keyboard SH card, and voltages leaking away from the capacitors.
Any suggestions or previous experiences of this problem welcome!
Thanks,
Lucid.
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