CYBERYOGI =CO=Windler

With home organs there are highend and household models. Things like Wersi Helios or Farfisa Maharani likely still find buyers, while a lowend Bontempi B370 (possibly even some Yamahas) gets scrapped. In a TV report they even smashed a >100 year old antique harmonium to pieces in a so-called "anger room" because nobody wanted it (the thing was pretty with lyra ornament, but had only 3 registers which made it unsellable).

Measuring -15V on a positive voltage sounds very malicious. My Nokia 417TV (low emission SVGA CRT monitor with high resolution PAL TV) had an atrocious design flaw the destroys irreplaceable special ICs. Namely in the power supply of the TV PCB it contains a positive and a negative voltage regulator. The positive regulator LM2940CT has an awful feature because it was designed to be also suitable for battery chargers, and so for safety (to protect against wrongways battery insertion) turns itself off if during power-on it detects any negative voltage residue on its positive voltage output. So if e.g. by moisture or leaky capacitors that line goes only slightly negative, it will selfdestruct because it output no positive voltage, and so current through the rest of the circuit pulls it even further negative, destroying the RGB amp IC and TV section microcontroller (which is impossible to find).

I guess it only would hum or increase other noises (keyboard matrix beep etc.) if 1000 instead of 2200uF was used. I can not imagine that this disables tone memory. If it was nF instead of uF it might have been possible, but the difference is not extreme enough to make it fail completely. This is not a supercap that holds enough charge to power a chip for days, any these old ones even ran warm and are nothing that runs on a few microamps.

🤔 You wonder about a CZ accordion? Then check out the Commodordion... 🙂

Desolder the transistor and test again. If any of its 3 pins have a low resistance short circuit, the thing is toast and needs to be replaced.

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.

If something digital plays dead, always check the reset capacitor. If it is decomposed or shorted (e.g. by battery liquid) the thing won't wake up at all or crash. Also faulty quartz or clock oscillator can make strange trouble.

What a crazy thing is this? The design looks like a bigger version of Casio DM-100, but according to the preset sound list it also seems to have a PD sound source.

Check the sustain pedal jack connections. Many early Casio keyboards play infinite sustain (until polyphony runs out) so long the sustain pedal is held. Hence a shorted contact or capacitor there would cause infinite sustain. Technically the sustain pedal is part of the keyboard matrix (simulating a non-locking button press) but likely has an additional transistor or 4066 IC etc. for decoupling it from the rest of the matrix (to make it DC controlled). If the part shorts, you get infinite sustain. In my Casiotone 401 with the "memory" switch the current chord is held after key release (with or without rhythm). The chord voice uses a different chip TMS3615, which analogue sustain length control voltage is at pin 3 (datasheet falsely claims 4). AFAIK in Casiotone 403 the main voice sound CPU is a D990G (a bugfixed D776G?, like in MT-60) that activates its "hold" (sustain) pedal through a diode from pin 17 to 25. The sustain switch is 17->26.

Nope, confusing polarity tends to destroy the CPU itself, so the thing is braindead (in Germany we call that now "vermariupolt" - as a pun of the word "verpolt" = "reversed polarity" and allusion to the name of the Ukraine city that was completely bombed away into ground). Battery leak vapour is mainly disastrous to LCD, the rest usually can be fixed.

Also Casiotone CT-7000 and RZ-1 had datasette "MT" feature. And for Casio PT-50 and PT-30 was the upgrade module TA-1 to save sequencer content on tape.

Do NOT use insulated cables - they are too thick and put even more strain on the PCB. I had badly messed up my VL-10 when I upgraded it with VL-1 functions and had to remove all that cable mess to use hair thin coil wires instead. To patch PCB traces, simply use individual thin copper wires from a wick cable. Also enamelled coil wire can be used (remove insulation by soldering iron heat before pressing into place). The graphite/carbon traces can be patched with copper wire too (resistance is not critical here). Only those directly under the black rubber contacts may suffer of oxidization or mechanical wear when soldered directly underneath (but they will function too). You may buy conductive carbon paint instead, but it is not really necessary here. Here I posted a photo of a patched PT-50 chord keypad PCB that got damaged much worse than yours. https://www.casiomusicforums.com/index.php?/topic/22041-pt-31-wont-power-on-where-to-start/#comment-84290

Perhaps midi pitchbend features may be used for this (at least if played from sequencer). But I don't know if normal keyboards support polyphonic pitch changes for individual held notes.

Did it ever suffer of battery leak? The corrosive vapours eat through the electronics (particularly in moist environment) and particularly damage LCD. But also copper traces and through-hole contacts of the PCB can go bad. Tiny black spots under the green laquer of a copper trace hint that it may have corroded through and lost conductivity.

The original CZ-101 and CZ-1 technology is fully understood and even found its way into MAME to emulate the inner working. So it would be time for Casio to build a modern remake with more features and perhaps a variant of the original engine with higher parameter resolution and perhaps control knobs and waveform display etc. I would be more interested in a classic SA-series remake with access to all internal sound parameters (important: without depending on any shortlived app crap and bluetooth radiation) and USB jack (midi and possibly USB stick support). IMO it should become a small but not excessively cheapish keyboard similar like Yamaha PSS-A50, so e.g. velocity sensitive midsize keys would be nice.