I just bought a Casiotone MT-70, that yesterday was fully working. After just a couple of hours of owning it and playing it a problem has occured :S
The C# and G on all octaves is not making sound and I can’t switch to the “piano” and “funky” tones. Here comes the weird part. When I switch the vibrato button from “delayed” to “on” they all work, but now the C and the F# on all octaves do not work, as well as the “flute” and “wah brass” tones. When I turn the vibrato off, everything works.
All of it was working 1 hour ago and the keyboard didn’t move or get damaged in that time.
Does anybody have an idea on where to start with this issue?
Looking at the MT-68 schematic which is very similar to the MT-70:
My first guess would be a bad connection on any of the cables that go to the keyboard and the panel. C#'s and G’s are all controlled by the same KI4 scan line, C’s and F#'s are controlled by the KI5 scan line AND the KIn lines also scan the switches on the panel. Hence … if you have bad contacts then bad reads are happening. Alternatively there could be a shorted diode pertaining to any of the switches, panel and/or keyboard.
So - I would start by just taking apart, clenaing re-assembling to start with