Repair of M-Audio MIDI keyboard

[adamburgess]

Hey everyone.

Friend of mine just dropped his Keystation 49 in for me to take a look at. My limited knowledge has me a bit stumped!

It has several non-sounding keys. Done the usual cleaning of contacts etc. No change. There's continuity with the lines between the keybed and the processor board.

Then realised, it's every 8th key that doesn't work (Bottom C, G#, E etc all the way to the top C) - so guessed a matrix problem.

My cheapo meter shows that all the diodes are at least passing current. Shorting certain diodes will trigger MIDI for all those notes - holding them all down at once, it can sometimes stutter a few notes.

What's left to try?

It's an old cheap thing and having already spent an afternoon on it, I'm at a dead end. Totally rebuilt a Kronos 88 keybed before Christmas which went so easily - but that was all mechanical damage - electronics were fine!

Thanks for reading!

[alistermorton]

Maybe the output that drives every 8th key or the input that reads them has failed.  Is it a dedicated kekeyboard scanner/control chip or discrete logic?

[adamburgess]

Looks like one microcontroller for everything. There is another chip on a daughterboard which looks like it does the scanning. Had another poke about this morning.

Can get a brand new keyboard for £100. Sad but probs easier to break the thing for spare bits - like keys which are always handy.
Not really worth anymore time on it, I don't think. And busy with gigs until New Year's, anyway.

[bruce]

Assuming it'll be something like an 8x8 matrix with diodes on each switch. Based on the (very few) similar units that I've repaired, if every 8th note giving issue, then it's an issue with one of the scanning outputs.

Bypassing the diode would have the effect you describe I think

Maybe one of the output lines from the microprocessor is shorted to ground or something like that?

[adamburgess]

Thanks, Bruce. Maybe it's worth another quick look after the weekend.