pt-20 Casio PT-20 plays notes normally...and then backwards?

[ericlimer]

I recently purchased a Casio PT-20 that was listed as "not working" and to my delight, some fresh batteries and the reset button brought it back to life. One issue however, whenever I play press a key, the note plays and then....plays in reverse? Holding down a key will cause the note to attack, sustain, and decay, then ramp back up to a peak before cutting off, as though the envelope is being applied correctly and then backwards. The length of the ghost note follows (but does not directly mirror) the length of the intended note: longer notes have longer ghosts. The ghost note for chords, however, appears to always be short. Here is some footage:

 

I have so far only done basic cleaning to no avail. The only notable detail I found was this white stuff on the board:  Is this indicative of failed capacitors? I would be more suspicious if the behavior of the keyboard wasn't so close to spec!

 

 

I'm going to chase down some leads from other threads on this forum, but I wanted to ask for any tips or ideas of where to start. I'm a little perplexed because the unit is not failing to produce sound or failing to produce correct sound, but rather producing the correct sound...and then some which suggests to me that the capacitors, at least, are all fine. But as I said, I'm new at this.

 

Curious for any thoughts or suggestions on where to go from here!

[CYBERYOGI =CO=Windler]

May be the melody envelope capacitor is bad (internal high resistance short circuit). In the almost identical PT-30 it is connected to pin 79 of the CPU D1868G (aka HD61703). Also battery leak acid spilled at its pins may have made the PCB material conductive at it and so short that pin.

Edited February 28 by CYBERYOGI =CO=Windler