I got the DX21 to make sounds and I have straightened out the keybed. I still can’t get some of the keys to work. I tried swabbing the contacts but the keys still don’t work. Would I need to replace the contact boards?

Maybe it would be worth resoldering any connectors or cables, connecting the keybed to the main board.

I recently watched a youtube video by Syntaur "Synth Wizards", where they did that on a DX1.

They just heated up the existing solder joint with a soldering iron (a pointy one, probably), and applied a bit more solder, so it would be fairly easy to do.

- Andy

I scrubbed the contacts again and I got more keys to work. I say it may have buildup on the FSR’s.

I just got another update. I got all the keys to play but whenever I hit C plus any note ranging from C# to E, it keeps playing all octaves simultaneously. I don’t know how to fix that malfunction.

Have you verified that with an init patch, just to make sure it's not some weird feature of the patch you're trying it with?

It sounds like it might be a keyboard matrix ghosting problem.? Keyboard matrix scanning relies on diodes, to stop phantom key presses happening when you press more than one key at once.

If you think of a matrix scanned in rows and columns - picture it as a grid - and you press keys closing three points, making three corners of a rectangle on the grid, it would be equivalent to pressing the fourth corner too, unless there were diodes there.

it's harder to picture how that happens with two keys at once, but I haven't seen the service manual or schematics.

So, I'd suggest checking the diodes that are part of the keyboard scanning circuit... there might be quite a lot of them, I guess.

Some multimeters have a diode setting, which shows you the voltage across the diode - typically 0.2V to 0.65V from anode to cathode, depending on the type of diode.?

If you don't have that sort of meter, just a volt meter, a 1k resistor (or similar) and a battery will do fine - connect the volt meter across the diode, and feed power from the battery to one end of the diode, completing the circuit from the other end, like this:

Battery + -> 1k resistor -> anode of diode
cathode of diode -> battery -

A single AA battery, or two or three in a clip, would be fine.

For a working diode, you'd get a voltage drop from the anode to the cathode, in that range - most likely around 0.6V.? If you don't get the reading, try the probes the other way.? A reading of 0V or significantly more than 0.6V indicates a dead diode.

- Andy

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I just got another update. I got all the keys to play but whenever I hit C plus any note ranging from C# to E, it keeps playing all octaves simultaneously. I don’t know how to fix that malfunction.

This sounds like a broken diode in the diode matrix.