Roland sh3a only plays a single pitch across all of the keys ; the onboard random sequencer, plays all of the pitches. I am stumped- please advise! 
Make sure that there are no key contacts that are stuck making contact. If one is making contact when it should not be, pressing new notes might be triggering the gate (i.e. playing a note) but the CV for the pitch will be stuck on that one note.
Well… visually, there are no keys engaged- to determine if two key contacts are engaged, will I need to open the keyboard up? Thanks! 
Just wondering if there might be some foreign object (e.g. paper clip) that fell down in between keys that could be making a shorted contact across key contacts, faking like a pressed key when none are. I’ve seen loads of debris in keyboards while rehabbing and cleaning them. My first experience was rehabbing an old “family” Hammond organ when I was in high school. You should have seen the pile of flotsam and jetsam I cleaned out of those 2 manuals (and elsewhere) including young children’s tiny toys. Kids love to stuff things in cracks. Pizza in the VCR player slot, anyone? Good luck!
Does the s&h play pitches above and below the constant note or is the constant note the highest or lowest of the s&h pitches?
I doubt that. The keyboard is mechanically quite impossible to get stuck. The same for the foreign object idea.
My suspicion is the wire which transports the CV from VCO board pin24 to the rotary switch for the “sampler” vulgo sample&hold switch. May be also the rotary switch itself.
I have an SH3a on my bench at the moment, so I may take some pictures.
Hey Fanwander,
Whatever came of this fix. I have an SH3a on my bench and Im having a similar issue, Where I cant get the keyboard to fire. Keyboard has power and all that junk. Was installing the Kenton Cv/Gate mod and everything was fine then it just stopped. Sample and hold works as it should and the synth works. Just know CV from the keybed itself. Ive removed the mod for now just to get it back to regular working form. Any insight would be amazing. Thanks !
I keep a dust cover on my sh3a when not in use, and don’t keep office supplies nearby… I have not opened it up, but no 2 keys appear to be stuck. what seems odd to me is that the random mode plays all the notes, otherwise, just one.
Did it still work after the CV/Gate mod was installed and broke later, or did it stop to respond to the keyboard as soon as the CV/Gate mod was in it?
Basically: the S&H has nothing to do with the keyboard control (it even disables the keyboard control). It will work always.
Well its weird. So after the install of the mod. It worked for about 5 minutes. Then the keybed just stopped. If I turned on the sample and hold. I could get notes to change through the sample and hold via cv. But it would still be pulsing the sample and hold rate. But the keybed now wont fire the synth. Im baffled. I removed the mod all together and put it back the way it was. But something got weird in there.