Need help to fix an old SH2000 Roland

Hi all,

First post here! Nice to meet you all. A good friend of mine gave me his SH2000 Roland for fixing it.
There’s 2 different problems with it.

First, when using, all sounds that have a sustain state (I mean all sounds that won’t die if you keep the key pressed). When I play then release a note then the first key of the keyboard will be triggered without I touch it. If I play a C then release the key then the lowest F (first key) will then trig.
I’ve been checking the connections of the keyboard and nothing seems wrong to me. I’ve also searched for any bad connection on ALL the connectors.
I’ve test ALL the diodes and find one that was faulty in the ADSR2. I changed it but I’m not 100% the one I’ve used is a possible equivalent.
My second problem is that I have a high pitched sound that is always preset on all sound even on bass sounds. Not too loud but quite annoying!
IS there anyone here that could help me investigate? I know a little in electronics. I’ve already made a lot of stompboxes and fix many machines but here I’m stuck.
If you can’t help me maybe you can tell me where on the net I should ask my questions.
All the best!

Hi again !

Time had passed and I’ve been working again on that problem.

Sorry but I’ve not described the issue properly in my first post.

Here is the problem with a better description:

With certain presets the pitch returns to the frequency of the first note of the keyboard when I release the key.
During Attack decay and sustain there’s no issue but as soon as I release the key the pitch switch back on the first note of the keyboard as if the pitch wasn’t maintained during release phase.

It’s reproducible ONLY with these presets => Bass Guitar/Hawain Guitar/FuzzGuitar1/Piano/Harpischord/Vibraphone/Planet and Growl

I’ve replaced many capacitors on all the board but not all of them yet and the issue is still reproducible.
On the OP12C pcb I did some measurements and I can see that on output 9 the voltage of current note drop as soon as I release the key.
Which part of the circuit manages the note during the release phase?

Even if you don’t know the SH2000 could you tell me where you would look in the first place ?
Thank you in advance for any response!

Have you tried looking for manuals for that Roland online? That can help out a little.

Have you looked at the keybed underneath and made everything is in order there? Sometimes a J-wires can get stuck above the bus bar. Perhaps your lowest key is stuck?

If not then I would suspect something in the “hold” circuit on the OP-12 board (page 6 of the service manual shows the schematic). This is the part of the circuit that stores the keyboard voltage until the next key is pressed. Transistors Q501 and Q503 would be some of the first I would test.

That’s a very neat diagram you found. Is that your personal copy or did you found it rummaging through the net?

Hey thank you all for your answers !
I was working with the service manual, of course ! It’s easy to find it on the web.
I’ve found the problem on the unit. Someone had made a weird shortcut connection (soldered) on the keyboard and it was the root cause of the issue.
I’ve been checking these transistors too and they are ok thank you @Travis
Now the synth is almost fully working, only the sample and hold stuff isn’t working as expected and doesn’t properly trig random keys. But this is not the most useful feature of the synth so I’ll live with that.
I’ve also an issue with the power switch. It’s supposed to switch +15 and -15 at the same time but someone did a filthy fix in the past. The power switch were actually switching only the +15v and the -15v was always on. I’ve removed the shortcut on the power switch and notice that this part of the switch was dead. I’ve added some contact cleaner in the switch and now it’s working again but I’m quite anxious with this. I Hope this will last but I didn’t find any replacement part for the power switch. So right now I’m using an external switch on the power cord…
I’ve also changed all the caps on the unit and I hope it will last !
Thanks !