Vintage Synth Explorer Forums

First off, welcome to VSE!

Second, there is a section called HELP which is devoted to issues such as yours, which I'm sure a mod will be along soon to remind/inform you of. most likely, the thread will be moved over there when that happens.

In troubleshooting any synth, the first thing you want to do is narrow down the culprit or offending section of the unit. this rules out other "healthy" sections, and makes fixing the thing possible, i.e. no sound on an analog might be a bad VCA, so running another synth through a filter input would rule out either the filter or amplifier. Digital synths, however, are a whole different world as they 'mostly' rely on DSP and groups of IC's containing entire voices, as opposed to discrete circuits handling functions independently. In a repair philosophy this is called "Component Isolation".

Keeping this is in mind, I would recommend isolating your issue of the C notes not sounding to determine whether it's a bad voice, or simply a bad key contact on the keybed, etc. So try plugging in a KGB (Known Good Board) controller via MIDI in (another synth or controller) and see if you can get the C notes to play from the controller; if you're successful with this, then the problem (hopefully) has nothing to do with the sound engine section of the synth and lies somewhere between the electro-mechanical section of the keyboard and the means of sending note information to the sound engine, possibly a bad relay for that group of contacts or short in the wiring itself.

Another thing you can try is to transpose or detune the keyboard a semitone, so that C registers as a C sharp, essentially shifting the note assignment over or up one key, and see if you still have the same problem.

Lucky for you, this board is FILLED with DIY'ers and synthtechs who not only repair but also restore vintage analog and digital synths (Maschinegeist, HFinn and Rhino, to name a few) so you're in good hands. Gentlemen, you have the floor .

hope this helps, and good luck...

Also, make sure that the V50 isn't set to one of its crazy tunings. I would guess that a reset would likewise reset this, but maybe worth checking.

I have the same problem, no tones from the V50 keys. I also noticed that the battery needs to be replaced as indicated on the diaplay. When the battery goes dead , the tones will be gone. Replace the battery, I'm sure the tones will function. Do a google search "Yamaha V50 battery replacement"
Hank

If it's a specific set of keys that won't function and everything else is fine, I strongly suspect it's an issue with the keybed. I don't know how the V50's decoder matrix is laid out, but if there's a single select line for all the Cs, and that connection gets broken, then this is what you'll see. Check the keyboard connectors and make sure they're properly seated at both ends; otherwise, you might need to break out the multimeter and start checking individual wires.

I will second what commodorejohn said. At the keybed check the connections and the pins they connect to. It may be a cracked solder joint from a previous owner's overzealous playing. You can use a multimeter set to continuity and check to make sure the pins go to actual diodes on the board. If you find that one pin connects to nothing that is probably your culprit. You can either solder a wire from that bad pin to the proper diode on the board and they should come back to life. You may also just have a bad diode messing up the matrix, so be sure to set your meter to diode and test each diode BOTH ways. If it passes signal backwards, then it is a bad diode that needs to be replaced. Worst case scenario is that it is the decoder chip, which is replaceable but a bit of a hoss to do so. Good luck! Those are very nice machines