IanB

Further to Chas's comment, I just found the VZ1 service manual and it does indeed have the output relay as he suggested. A likely culprit!

Number 2 might well just be poor contact in the connectors. Easiest way to check this would be to open it up and tap a signal direct off their connections to the PCB and see (er, hear) how that sounds. When op amps fail, they usually fail completely. It's also possible the circuit board is cracked by the connectors- inspect closely with a magnifying glass with a light source arranged to cast shadows. As to the contacts, I'm not familiar with the mechanics of this device, but is the rubber still springy and in good condition?

It might just be a bad internal cable connection if it's intermittent.

Agree with Chas's comment. Also to add that looking at the schematics, the 9V heads straight into several voltage regulators internally, so it's probably pretty liberal about the incoming voltage. Bear in mind that the voltage of an old fashioned power brick is only a nominal voltage and can be much higher depending on its loading- so if you measure the voltage when it's not powering anything else the voltage will be significantly higher.

I just thought everyone would enjoy the virtuoso playing of Bob Green, The Jazz Engineer.

Basically, it should sound like this.

Nice!

"The mainboard needs replacing" means "I'm not willing/able to do a component level repair". I wonder what the actual reason for it is. That the error in the video moves with octave selection is very intriguing.

@Paolo70 What happens if you use the CT640 as a MIDI controller for the other keyboard, that is you take the MIDI OUT from the 640 and connect it to MIDI IN on the other keyboard?

@TomAgainHonestly learning to repair stuff is very satisfying, and it's stuff you can learn bit by bit. You can do a lot with just a cheap multimeter and an audio probe (a wire connected to an amplifier input so you can "listen around the circuit"). And there's something very satisfying about soldering. The nice thing about this older gear is that the components are quite large and "human sized" compared to modern stuff. Of course we all only have time in life to learn some things and not learn most everything, but there are worse things to learn than electronics

Hi Tom, this will be a problem with the electronics, and changing the fuse (which fuse?) won't do anything. The CT701 contains three separate tone generator circuits, one of which does the right side of the keyboard, and it sounds like there is a fault with that tone generator. Unfortunately unless you can do fault finding or can find someone who can do it, there's not much you can do. You could maybe open it up and have a look to see if anything is obviously frazzled, and unplug and replug all the internal connections in case one is not seated properly. Here is a video of somebody opening up a similar CT602

Hi Tom. It's always hard to tell from a description, but it's likely this is an electronic fault. The 701 was a pretty complex design with several LSI chips generating the tones digitally. If you've tried all the usual things like flipping all the switches, this would probably require experience with electronics and some test equipment. Does the melody/accompaniment balance control do anything?

Relating to Brad's comment, it sounds to me simply that the headphone jacks are in parallel, so what goes in one comes out the other. Same as using a Y splitter.

My instinct is that this isn't the opto. Let's see

Brad Saucier: THE LEGEND IS REAL! 😆

I have several 1/4 to 1/8 inch adaptors that often get used for this purpose, as dummies to stick in sockets. I've always presumed that the manufacturers avoid having a setting so people don't think the speakers are broken.

According to the service manual, the board should be labelled either MA2M or CN5M. Where is it labelled "B" or "C"? Giving us a photo always helps

@Jokeyman123 Agreed. I extended my knowledge to repairing CRTs (something I'd avoided due to the voltages involved) when I found it effectively impossible to find anyone who would repair one. I suspect even a lot of modern monitors are getting thrown away due to nothing more than a poorly seated ribbon cable. Considering the number of people out here keeping decades old equipment working- old Casio synths and the small keyboards we all love being notable on this forum- we need more expertise than swapping boards, the supply of which doesn't last long beyond the launch of the next model anyway. I'd better shut up now or I'll start ranting about the difficulty of getting service manuals etc, which manufacturers these days seem to clutch to their chests like firstborn infants. Which reminds me, I really need to strip down my (20 year old) Roland MIDI controller and give the key contacts a clean.

It sounds like the technician didn't try very hard or was not that competent. There are many "technicians" out there it seems who can't do more than change a simple component like a switch, or a board swap. If the PSU has not been changed, this would be the first avenue of inquiry. Might also be a faulty internal capacitor in the keyboard itself. The behaviour you describes smells strongly of a capacitor issue somewhere. "It's the main board" may well be a euphemism for "I don't know what's wrong". Most people faced with that kind of replacement cost will just buy a new one, which saves the tech the embarrassment of not knowing what is actually wrong with it.

It's important to understand what a host is. USB is a master/slave protocol in which the host is the master and the device is the slave; bear in mind it was originally for connecting things like keyboards and mice to PCs. The host contains most of the brains and controls the communications; the device (slave) only has enough brains to send back simple replies. When you plug in a device, an initial "handshake" is initiated by the host in which it asks the device what it is, and the device reports back, "I am a mouse" or "I am a controller keyboard". The host then sets up a suitable messaging protocol so it can receive information about mouse movements or button clicks, or MIDI-type musical information. So it's a very active means of communication and the host entirely manages that. This is why USB cables have a different plug on each end, so that you can only plug a host in at one end and a device in at the other. If you did use a simple connector adaptor to make an "illegal" connection, it would be like plugging a mouse into a keyboard and expecting them to talk directly with each other. They can't; neither of them knows anything about the other. It's just not how the system works.

@CYBERYOGI =CO=WindlerYes, my mistake, you're right about the patent. I found it some weeks ago when researching vowel-consonant and failed to appreciate the difference with the more simple engines on the keyboards like the PT-20. Oops😕

No problem Dan, any more questions just ask!

By the way, this is one of the original Casio patents describing the square wave generator and processing etc. https://patents.google.com/patent/US4590838A/en?q=synthesis&inventor=Toshio+Kashio

@CYBERYOGI =CO=WindlerYou deserve much kudos for this depth of investigation and elaboration!👏👏 👏👏 👏👏

You can't do it that way unfortunately. Casio's choice to put USB on all their keyboards means they have to be connected by USB to something which will act as a "USB host"; a computer, tablet etc. A normal USB/MIDI adaptor cord (see below) won't work, you'll find it has the wrong type of USB plug on it, designed for a computer USB out rather than a device USB in. You can get a standalone host unit which will act as if it's a computer e.g. this one https://miditech.de/en/portfolio/usb-midi-host/ Alternatively you can connect to a PC etc with a normal USB cable, then use a USB to MIDI converter also plugged into the PC to connect to your MIDI synth's normal MIDI (5 pin DIN) connectors. Do however beware of cheap generic USB/MIDI adaptors which do not work properly (they do not transmit all MIDI messages) and they are also not electronically correct and can allow damage to devices (they do not contain an opto-isolator as per the MIDI specification). There are many like these on Amazon, all based on the same "bad circuit" and you should avoid them- https://www.amazon.co.uk/OTraki-Interface-Premium-Converter-Keyboard/dp/B07KYDP3GK/ref=sr_1_5?crid=HZ8T0SDZDI5A&keywords=usb%2Bmidi&qid=1657866220&sprefix=usb%2Bmidi%2Caps%2C94&sr=8-5&th=1 Look for a good name brand like Roland, MidiSport or Behringer. The Roland UM-ONE is a "cord" solution and works well. I've got one in use on my PC as I type this. But as I said, this is to interface to a PC, it won't work standalone. https://www.amazon.co.uk/Roland-UM-ONE-mk2-MIDI-Interface/dp/B00967UN50/