IanB

Keep us posted @Rookierafa🙂

So here is what I'd likely do: connect your meter, measuring voltage, securely to the output of the 7815 voltage regulator- you may have or may need to obtain crocodile clips that slip onto the multimeter probes. Starting with the main board disconnected, turn the power on. You should be reading -15V. Now plug the main board in and see if the voltage drops straight away to zero.

Hi @Rookierafa are those resistance readings? This isn't something I'd really be checking at this stage. I'm speculating at the moment that there is a short circuit somewhere on the main board causing the negative regulator to shut down. Likely culprits would be either a physical solder "bridge" somewhere (have you soldered anything on the main board?) or a capacitor or possibly transistor which is short circuited. Try doing a continuity test on the main board, while it is unplugged, between the incoming regulated voltage rails and ground. If either is shorted (it "beeps") that will be useful although it probably won't be that simple. It's a bit strange that this all started with the PSU suppression cap blowing but that might be a red herring; possibly blew open circuit years ago.

A good Easter to you also @Rookierafa and I'm sure we'll get this sorted. Will post more thoroughly later (just got home from work, rather tired) but two types of transistor are "ordinary" bipolar ones with the base etc and FETs with drain etc. The power amp has its own supply that doesn't run through the 7815/7915 regulators. It's the outputs at the top of the PSU diagram on the right labelled +VA and -VB on the diagram (but apparently +VA and -VA on the actual PCB.

OK so that's progress. As I said previously, the 7815 will shut down if it sees an overload/short on its output (they are well designed to avoid blowing up). So likely there is a short on the main board somewhere. This might be a physical short circuit, or may be a failed capacitor, transistor or some other component. I'm about to head out to work but I'll take another look at the circuit diagram this evening when I get home. The power readings on the main board will be doing strange things because the negative is basically disconnected when the 7815 is in shutdown.

Hmm. The output of the fuse, the capacitor and the input of the 7915 are all directly connected on the circuit diagram so should all be at the same voltage, it's the -VCC fuse. You said you have measured the voltage at the fuse but didn't mention checking the fuse itself. Is this voltage at both ends (i.e. is the fuse good or blown)? If you have your 27V at the fuse out terminal, then either the PCB track is damaged or the 7815 has a dry solder joint. Take out the fuse and check its continuity with your meter. With power off check you have continuity from the fuse terminal to the 7915 input (centre pin) and also to the capacitor's -ve terminal (I assume it's the capacitor nearest the 7815). Can't think of anything else to suggest right now...

Ok, so it looks like you have no output from the 7915 you replaced (it's a voltage regulator not a transistor btw). Check what voltage you have on its 3 pins. The input is the centre one (2) the output is the right one (3). Is it bolted to the case or a heatsink? Its metal tab is connected to its input so if the heatsink is not isolated or it's bolted to common metalwork it should have an insulating washer. If it has no input, check the fuse before it and the bridge rectifier before that (feel free to post a photo of it). You probably have +15V on both pins of the op amps etc because there's not voltage supply on the negative supply pins at all so the +15 is just backfeeding through them. Also note that the 7915 has internal short circuit protection so it may be fine, but is shutting itself off due to a short circuit on its output, so it may not be the culprit but we will start there. If you can disconnnect the PSU outputs from the other board(s) to check the voltages that would be useful to do for that reason. If there's -15V on 19/brown when it's not connected to anything else, the problem is further down the circuit...

Just to clarify, what's the voltage on pin 19/brown coming out of the Power supply?

Maybe not even corroded, just not making connection properly. Some problems can be fixed just by unplugging and replugging, or waggling, connections. Such problems can be hard to declare "fixed"!

Such problems can be hard to track down, let's see how it performs in a soak test i.e. leave it on for a long time and see what happens.

Have you had a look for the output relay?

"Anthem" is the right word!

If memory serves, there is no power relay, the PSU has a lot of circuitry to test before powering up but it's all transistors and logic gates. The relay just connects the audio output after power up to prevent a "thump". So it sounds like there is something dodgy with the power which is also killing power to the relay as it is intermittent. Seems likely to be a bad solder joint or connector if it works sometimes...

The main weakness of the original implementation was the lack of real time parameter control, you had to repatch to change anything. That would be easily do-able now.

Very, very good question. As a Phase Distortion Synthesis fan myself I'd love to see this. And with modern technology, it would be possible to make it much more flexible- the original implementation was limited by the digital circuits that could be run on a chip fabricated at that time, it's all counters and look-up tables if you look at the patents. I've written a plug-in (not released yet) that has my take on a more flexible PD synthesis with real time control, variable "resonance" etc. I'd love to see Casio release a new CZ.

The electronics will likely be fine, though should be cleaned before use. The major concern would be anything absorbent like felt pads. The best thing to do would be to open the piano up and take a look (and some pictures, so we can have a look as well!)

Do you have any test gear? Multimeter, oscilloscope, etc?

Does the actual power go off, or does the audio just stop coming out? The clicking will be the relay that connects and disconnects the audio signal which is a well known point of failure. If all the power seems to be going off, I would open it up and wait for the failure to happen, then get a test meter on the power supply board and see if it's actually producing any voltages. That will narrow it down. The PSU is fairly advanced with a number of signal lines to the rest of the synth to check "OK" before it actually powers it up. I have schematics if you'd like me to post them.

If you can hear the notes but they are very low, there's a good chance this is in the internal mixer (audio circuit rather than digital circuit) which should make it relatively easy to fix with appropriate test gear. Might be a failed op amp or even a bad DC blocking capacitor.

Another update- V1.1.11 Changed DCO controls to give an "Off/On" setting for 2nd Waveform, as is used on onboard CZ synth parameters Bugfixes: Detune fine setting was only covering 1/4 of the range (incorrect bitmask) Crash if first item in an Envelope was set to "End" and you clicked delete. ---------- Turns out VZV-CZ was only covering 1/4 of the range of "Detune Fine" and none of us noticed until user Gary emailed me (the Sysex protocol has two extra bits tacked on the end of that value). Luckily doesn't affect any patches saved out of CZ. There's always another bug...

Yes. I think my point was that any part of traditional instruments can be fabricated by a sufficiently skilled craftsman. The problem with electronic instruments like this is that they rely on the availability of commercial elements which cease production and can't be fabricated without a massively expensive production run, particularly for instance the Casio LSIs. Now currently we do have the option of microcontroller and FPGA emulators... but often we don't even have the specifications of the original device.

Ah, the legendary troublesome CZ relay..! To be fair, they have lasted well over 30 years. Considering the continued popularity of "vintage" keyboards, I wonder how long the designers anticipated them being in use for, and indeed how long the electronic musical instrument designers of today expect their wares to last. Acoustic instruments can last indefinitely and can pretty much always be repaired by a craftsman. With electronics, it's a different story. It's sad to think they'll all fall silent in the end however much care they get.

If you don't know if you can repair it, the answer is no I'm afraid. Modern day power adapters are quite complicated and you need the electronics skills to understand them. The chances are anyway it is simply kaput. Usually when they fail they are beyond economic repair. You should obtain a new one.

That makes sense from Casio's POV since the accompaniment is "automatic". Turning it into a MIDI file would mean the "operating system" would have to run through its accompaniment and "decode" it, which would be a pointless waste of effort. You could assign some MIDI controllers to that to start, stop and change the accompaniment though. But whether anyone would actually *want* that is another matter

@Summers It looks like it's this one-- https://support.casio.com/en/support/download.php?cid=008&pid=72 Not updated since Windows 7, but hopefully still works on 10.