Well, after cleaning the PCB which made a small but insignificant difference, I ended up doing this exact modification to a CS-60 this week, and am happy to say it worked. Long release times on Sustain 1, and the pitch stays exactly where it should.
I'm just surprised that more people haven't commented on this problem, as it would seem to be fairly widespread - if the CS machines that I see are anything to go by.
A friend of mine has just acquired an absolutely beautifully preserved CS-60, even the chrome trim around the edges of the case looks like it just came from the factory. I shall be interested to see if that one has the Sustain 1 problem.
Lucid.
----- Original Message -----
From: jkjelec@...
To: yamahacs80@yahoogroups.com
Sent: Tuesday, May 17, 2011 10:38 PM
Subject: Re: [yamahacs80] Pitch Drop When Using Sustain 1
I had this problem with a CS-60. Several of the voices were leaking like this. I had changed all of the relevant parts that could result in sample and hold droop, but the problem remained. I cleaned the PCBA using alcohol, but it didn't help. I suspected it was the PC board leaking, and had independently considered doing the modification you posted. However it wasn't my synth; I was repaing it for someone. I thought just how bad it would look if I did this massive, ugly modifcation, and it didn't help in the end. So I told my customer I couldn't fix it.
Then I saw your post, and I was thrilled to see you had licked this problem. Strangely enough, the customer ended up moving to a different area of the globe, and the problem seems to have gone away on its own! I suspected that the synth was now in a dryer area, and so the the PCB had "dried up" and stopped leaking...but the customer says the new area is humid, and so I am scratching my head.
I think the CS-50, 60, and 80 all use the same SH board (the CS-50 only has 4 of 8 circuits populated), so I think the problem could occur on all of these units.
Regards,
jkjelec
----- Original Message -----
From: "lucidsound" <lucidsound@...>
To: yamahacs80@yahoogroups.com
Sent: Saturday, May 14, 2011 4:31:02 PM
Subject: Re: [yamahacs80] Pitch Drop When Using Sustain 1
Good grief, did I write that? If I did I'm glad someone preserved it, my memory is not what it was.
I'm still interested to know if anyone else has this problem with a CS-60 or CS-80.
Thanks,
Lucid.
----- Original Message -----
From: jkjelec@...
To: yamahacs80@yahoogroups.com
Sent: Saturday, May 14, 2011 9:13 PM
Subject: Re: [yamahacs80] Pitch Drop When Using Sustain 1
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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