IanB

Hmm, if you've already got dead transistors T11 may be suspect, if you can replace it no harm in doing so. T8 and 11 are acting as a darlington pair so this implies to me T11 is faulty. Variable resistors shouldn't be "bouncy" at all but the JFET may be causing that, you'd need to desolder it and test it out of circuit to test it properly.

Might be worth asking your friend again First thing to check is that the op amp actually has power. It's possible the amp board has no power.

Hmm, this is very hard to diagnose without being "hands on". The simplest explanation is your probes aren't making good contact, but other than that it might be because there are other voltages present in the circuit. Or something intermittent- dry joint, cracked trace, etc. Bottom line is, blue to red should be a straightforward 0 ohms (or near enough) short circuit.

This might seem like a daft question, but you have taken the batteries out, right?

I don't think the diodes are the problem, they're just steering the battery supply and we know power is coming in okay. 1N4001s would be fine, they're just rectifiers, but ignore them. Something isn't making sense: reading back, the V+ can't get onto BLue if it's not connected to Red, so either your voltage measurement or continuity measurement must be incorrect. With the machine disconnected from power, test resistance from Red (either end) to that star point of circuit traces we can see in the photos on the power board. You should get about 100 ohms, and if so we can discount problems with the power switch. I'd generally advise against over-enthusiastically swapping components and resoldering things as this can introduce new issues on top of the old one(s). A while ago I bought a Fostex 4 track on Ebay that somebody had decided to replace all the capacitors in and rendered it completely non-functional!

@momo Yes, according to the schematic there should be 0 ohms. It seems to me (anyone else reading this, am I right?) that the sole purpose of BLue is to act as a pulldown via the 100R resistor (connected to ground) which enables the Power On pulse at A etc to function. The White wire ultimately connects to there, if you trace the diagram. As far as I can see it discharges the capacitor that does the pulse. The thing to do now would be to trace out what is happening with R and BL on the little CN5M board. You might just have a bad solder connection. Feel free to post explicit pictures of the board

Thanks momo, just looking at the circuit BL should be physically connected to R, if you look at the schematic you can see that on the power switch's little board M4152-CN5M on the lower right of the drawing. So blue should be the same voltage as red. Can you check continuity between them, with the power disconnected, then measure the voltage again with power off and on? Also all these middling 3.6V measurements suggest to me the chips aren't powered and are just floating.

So anyhoo, looking at the service manual I think a first step would be to check the voltages at the marked test points on the power board. Most of these can be checked with a multimeter, for instance point D should go high when you switch on and stay on until you switch off, point E should go low, F should go high when you switch on and off (after a 5ms delay, too short for you to see) when you switch off. Measure the voltages at each of these test points with your multimeter and make a note of what they do as you switch on and off, and report your results back to us Point "G" is a really useful test point as it's the output of the voltage regulator. Also check you've got power coming in and out of the power switch etc

They should be interchangeable, those letters are various options like whether it's lead free, etc. These chips can be damaged by static so it's possible your replacement was also faulty, you could test it on a breadboard but it's probable the fault is elsewhere, so I doubt very much ordering the BE (that's the standard designation, it actually just means buffered input which are standard) will help. There's a lot of discussion in this thread of what voltages should occur where during startup etc, I know it's tedious but I would advise reading the whole thread and see if it's any help. Otherwise we're starting from scratch again

@momo Well the short answer is, try replacing it and see if it works. It can't make things any worse. If you do, put the IC in a socket rather than soldered to the board. As far as testing goes, if you look back up the thread you'll see that it's a quad NAND gate, so for each of the gates, taking both inputs HIGH should make the output LOW. It does sound like a similar power board problem. I'd try this and see if it works.

In my view this is because the "traditional" subtractive analogue synth is a distinct instrument in itself, something I've always believed since the 80s. I think many people saw it as a failed attempt to sound like "real" instruments which was why the horrible abandonment of them after the dull, dull DX7 came to market, thankfully they were revived by the "Rave" movement. Analogue sounds- filter sweep, resonance, pulses and sawtooths, have their own special sound and people love that. I do get a bit irritated by the present tendency for analogue to fall into the "audiophile" style purist mindset sometimes, there's quite a lot of nonsense written about circuits that are just bog standard as if they contain some sort of magical elements but hey ho, at least they're being appreciated.

This might be due to a wiring issue with your home wiring or an extension cable. Considering it sounds like a limited current, it's probably some form of leakage current which can occur if something which should be Earthed isn't. What country are you in with what voltage and plugs (2 pin, 3 pin, 2 pin + Earth, etc)?

@mrmr9494 thanks, and I admire your program also, looks like it was a lot of work! I originally wrote mine for my unusual niche that I had found out how to patch my CT6500 (which is the preset "home keyboard" version of a CZ) but there was nothing available to support that and manually editing sysex files was ergonomically unreasonable Then it sort of grew into a general editor and patch manager for CZs. One thing I like about distributing it through the Microsoft Store is I get to see it being used all over the world through the analytics available. As an aside, I'm currently writing PIC assembler for my homebrew monosynth and deep in decoding the MIDI data, I've had it just responding to Note On/Off for a while but getting into all the other stuff- pitch bend, controllers, sysex etc has me at that "bigger job than I anticipated" stage. Gaah.

Standard MIDI never needs a special driver for the keyboard because it is a simple serial universal protocol which does not change from keyboard to keyboard. Either the keyboard isn't sending MIDI (is faulty) or your adapter is faulty or there is a software problem with the adapter. Make sure you have everything hooked up the right way around, it can get confusing with MIDI In and Out; the keyboard Out connects to your adapter In and the keyboard In connects to the adapter Out.

As an amateur developer, I made the choice to go with Win10+ only for my CZ editor software. If I wanted to be compatible with earlier Windows like 7 and 8 I'd need to keep a PC running those OSs just for testing and that's more effort than I care to make, having upgraded everything I have to 10. This excludes some users but we all have to make choices in life. I was very fond of Win7 myself, but staying with it would ultimately exclude me from running newer software.

Sounds like it needs a squirt of switch cleaner.

My Roland PC180A MIDI controller (bought sheesh about 20 years ago, early 2000s!) has springs (at the rear of the key).

I dunno, I think that CZ101 has a certain punk appeal to it 😁

@Chas I think it's a pity that they didn't move forward with PD. They went next with the VZ series which tried to be more "DX like" in programming and didn't catch on. OTOH a version of PD with real time parameter control and more flexible modulation would have been killer. Come to think of it, that could be done now, or at least something sufficiently similar, without the massive expense of custom chips that was required in the 80s. Might be a possible "fan project"!

I don't know this keyboard but as general advice, it would make sense to plug the CTK into a PC and use MIDI-OX or something similar to see if it's sending MIDI sync messages. With a problem like this it's best to try to break it down into smaller problems.

So, eerily similar to the CT6500 thread with its "1Hz timesharing", i.e. the CPU assigns notes to Music IC A for one second (or so) then assigns to Music IC B for one second, back and forth. If each is handling a maximum of 4 notes polyphony, holding down 4 keys and then pressing another forces it to assign to the other IC, which is the one with no output. So yes, either one chip is dead, or its support circuitry is faulty somewhere, or something is dead in its audio path before the two chips' outputs are mixed...

If the code or just a description of the protocol are available I can write code to run on a PIC microcontroller, are these available?

To echo others, please look after yourself. The rotting that comes with ageing is the dark part of the human experience sadly. I hope you will start to feel better soon, we are all with you here. The project looks amazing! May I ask what that little USB board is? I presume it's some kind of converter to talk to lesser microcontrollers?

@Aaron WrightHopefully you'll be out of N00b Quarantine soon!

Regarding the strange sound- it may be that it's fine if both keys are sounding on the same 933 but not if they are on both 933s, or vice versa (fine on different, bad on the same). You could disconnect one of the op amp channels at a time and see if you're still getting overdrive. BTW if you haven't socketed the TL082, now would be a good time to do that for ease of fiddling.