Loss of Velocity Sensitivity - but NOT a mechanical problem

[jdcaudle]

I've got a Casio CDP-130. I'm posting here instead of the Casio Forum because it's possible someone has had a similar problem with another brand.

While I was playing, a range of 8 keys suddenly lost velocity sensitivity. After a short while the next 8 lower keys lost it as well, but regained it after some more time.

I've taken it apart and cleaned it - even removing every key to get at the contact sensors. The rubber contact strips are in good condition and clean.

I noticed each key has two contact sensors - the rubber pads that the keys hit each have two conductive pads: one is longer than the other and would contact first. I assume that velocity sensitivity is achieved by measuring the time interval between the two contacts. I tested "normal" keys by closing only one contact at a time - no sound. Only when both contacts are closed is there sound. When I do this on the "defective" keys I get a full velocity sound just from closing either one of the contacts.

The circuit board the contacts are on looks pretty simple - no ICs or anything, just what appears to be a single transistor for each key. There is no visible damage and the solder joints look healthy on all the transistors. The ribbon cables look good too.

In addition to the mechanical inspection and cleaning mentioned, I've tried every velocity sensitivity setting, cutting power for an extended time, and what was suggested somewhere online as a factory reset (though there was no indication anything happened when I did that).

Any suggestions?

 

[happyrat1]

The problem is that between the octaves missing velocity and the multiplexer you have either an open circuit or a blown driver transistor or chip in between.

Try and trace the circuit back to the driver chips and see if you can narrow down the open circuit to a specific trace or solder joint using an ohmmeter or a continuity tester.

If all the lines have continuity then you probably have to check out the driver chips on the motherboard.

Either that or else when you reinstalled the rubber contact strips you reversed them which can also explain this behaviour.

Gary

It could be as simple as a defective ribbon connector. Those things are difficult to eyeball without a tester.