JX 3P Stuck note problem?

[James Mandible]

So I've had this JX3P for about a month now with no problems. Suddenly today I turn it on (after it being fine yesterday) and notice that it seems to be ALWAYS playing a note. Not from first startup really (it makes a weird sound at startup, almost like an lfo modulating something?) but as soon as you press a key, any key, it gets stuck on it, almost as if the hold button is always on. The hold button light isn't on, there's nothing plugged in to the trigger sequencer jack or any of the midi ports. Any ideas?

[synthparts]

Try plugging a cable into the hold pedal jack and see if it goes away. Is it on all voices? It could be a dead VCA stuck on (BA662A chip - I have them).

[James Mandible]

Plugging a cable into the hold jack does not seem to help.

It seems to be one voice at a time. The first key you play will be super loud and the others will play muted. After several key presses it will trigger another loud sustained note and start over. The problem is not consistent with any particular key and does not seem to be corresponding to every six notes or anything like that, so I'm guessing it's not a voice chip?

[James Mandible]

here's a recording of the problem, from 1-5 seconds you'll hear the modulation I was talking about, and then when a key is pressed.

[Don T]

here's a short list of where to start:

1. Check the power supply voltages per the service manual.

2. Unplug, then plug back in, connectors CN8 and CN9 (bottom right corner of main board).

3. Check the wires from CN8 and CN9 that go under the keyboard. Make sure none of them have rubbed through the insulation and are touching the metal keybed frame. This is not likely, but you want to cover all the bases.

4. Lightly moisten your finger (and I mean LIGHTLY), then touch the top of IC45, then IC46 (They are next to CN8 and CN9) to see if they are noticeably hot compared to any of the other chips. Do the same with IC9, IC10, IC11, and IC12. These last four send the gate/ADSR signal to each VCA.

If none of the above does any good, or if you feel either IC45, IC46, or IC's 9-12 get hot, let us know.

The VCA chips are IC101, 301, and 501. Each voice shares one half a chip. They are normal 4558 opamps driven by a C945 transistor. I'll post a pic later on where to check to see if one of the VCAs is stuck open as Synthparts suggests.

[James Mandible]

thanks for the tips, I will try to get around to opening it up later tonight

[James Mandible]

IC12 is noticeably hotter than ICs 9-11 + 45, 46

Everything up to then was done, checked and the problem is still there.

[Don T]

IC12 is noticeably hotter than ICs 9-11 + 45, 46

Everything up to then was done, checked and the problem is still there.

Then either that chip is dying, or something that draws current through it is faulty. I'll dig through the schematics again, that is if I ever get finished with calibrating the %$#!%#$@ OB-Xa someone brought in...

[James Mandible]

Anyone know where I could get a replacement IC12?

[synthparts]

I have them.