Hi there,
I've got a Yamaha tyros 4 in for repair and the keys seems to have a mind of their own, some keys make sound, some comes out on full volume, some keys remains to sustain long after the key is released and some don't even make sound. Its not consistent meaning the same note does not behave the same all the time.
The keyboard had some issues in the past but it was typical velocity/dead keys and cleaning the rubber contacts solved the problem. However this time it seems this is not the case, I did clean the whole keybed nonetheless and to no surprise it didn't solve the problem. Did a factory reset and it didn't solve the problem either.
So I took out the oscilloscope and probed the scanning pins. Here is what I found:
1. All the pins marked BK (BK00-BK13) shows a nice square wave, with no noise. The 'on' time is longer than the 'off' time.
2. Pins marked with MK does not show a steady square wave but a weird 'spiky' wave - like a weird 'saw-toothish' wave. MK24 was the worst, also on one MK pin(can't remember which one) it showed a square wave superimposed over the wired sawtooth wave.
I couldn't probe around the IC as I would have to disassemble the whole keybed. Was hoping I could get your guys advice on what to look for next and what could be the probable cause for this fault.
Appreciate the help.
I've got a Yamaha tyros 4 in for repair and the keys seems to have a mind of their own, some keys make sound, some comes out on full volume, some keys remains to sustain long after the key is released and some don't even make sound. Its not consistent meaning the same note does not behave the same all the time.
The keyboard had some issues in the past but it was typical velocity/dead keys and cleaning the rubber contacts solved the problem. However this time it seems this is not the case, I did clean the whole keybed nonetheless and to no surprise it didn't solve the problem. Did a factory reset and it didn't solve the problem either.
So I took out the oscilloscope and probed the scanning pins. Here is what I found:
1. All the pins marked BK (BK00-BK13) shows a nice square wave, with no noise. The 'on' time is longer than the 'off' time.
2. Pins marked with MK does not show a steady square wave but a weird 'spiky' wave - like a weird 'saw-toothish' wave. MK24 was the worst, also on one MK pin(can't remember which one) it showed a square wave superimposed over the wired sawtooth wave.
I couldn't probe around the IC as I would have to disassemble the whole keybed. Was hoping I could get your guys advice on what to look for next and what could be the probable cause for this fault.
Appreciate the help.
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Appears to be a key matrix problem. I had similar issue with a Yamaha keyboard years before and could not solve. It is always like the 5th time a key is pressed, no sound. Other 7 presses are OK. If you press same key 8 times, it will fail on every 5th press. Happened only with Yamaha keyboards. On Korg keyboards, was able to reload the internal tone memory card and got solved. Best of luck. Regards.