Yamaha P-125 Crazy key behaviour

Synth Repair
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[Yamaha] [P-125] – [Crazy key behaviour]

Yamaha, P125, key issue

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Someone brought me this P-125, it’s a P-125B to be specific and it’s in great physical condition but it has this crazy problem. See the videos below. If you hold down a chord like a triad the last key starts to auto-repeat. It happens across the whole keyboard. Depending on which keys you play it might take 4 or 5 keys to be held down when the last one starts to auto-repeat. It doesn’t do it with only 2 keys, the minimum is 3 and then it’s specific, play D, G and C above it anywhere on the keyboard and it does it.

I’ve cleaned the keyboard strips and resoldered the keybed PCB headers. No result

It doesn’t do it over MIDI at all.

There’s a keyboard scanner MCU on the mainboard that’s my main suspect but they don’t sell it on it’s own, have to buy a mainboard but it’s not cheap, customer agreed to it but I have to be sure it will fix the fault. What you guys think?

See videos

1 Like
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You said it doesn’t do it over MIDI, so sounds very much like an issue with the main board.

3

A quick search shows multiple keyboard issue videos with the P125 for clunky keys, and the solution is to grease the keybed. My money is on grease has gotten into a contact somewhere, and causing a shorting.

I would further speculate the grease was a conductive brand, not dielectric (non conductive).

I would look again for where grease could short out a keypad, because the problem does not repeat with midi.

4

Thanks for the reply but I cleaned all the key strips and keybed PCB. There was no grease.

5

Check the main board and power board for any spills and or corrosion setting it. Look at the IC’s leads that attach it to the board if any are darken I would call it a bad board. Replace it. Good luck!

6

Use a strong magnifying glass and a bright light and search around the RAM chips for solder splatter from a previous repair. Check the board for stains from leaky Caps. Clean the board.