Why is my yamaha psr 225 keys not working?

But many keys in a random sequence isn't working, if it was related to connection the all keys connected to the loose connection should not work, but the case is different

@ASTRO1 PIANIST

What do you mean by random sequence? That they work sometimes and then not at other times?

You never mentioned that they were working in a random sequence. All you said was "....some keys are not working....", so my answer was based on your description of the problem in the question you posted.

The connection could be coming and going as you're pressing the keys making the connector move so that it works again for some but then not for others. Loose connectors can cause all sorts of varying symptoms.

It was only a suggestion.

Start gently testing with a voltmeter or a test lamp, so as to not cause any movement.

Each key should have power supplied to it from the processor control board.

If it is varying or disappearing and then coming back you have to go back to the source of the power on the CPU control board and go forward from there to the keys.

Use the manuals from the answers in the link provided above as they're all essentially the same circuit for the keyboards. At least it is better than having none at all.

@ASTRO1 PIANIST

Have you checked under the keyboard keys where the boards are located?

Have read that is where all the diodes that electrically separate the keys for the different notes are on a strip and if the keyboard is bent it puts pressure on the strip and shorts them out but not totally sure that this is your problem.

Given the wide range of the notes as far as the wiring goes it puts the problem back at the control board.

Sorry i can't be of more help as without a schematic it is difficult to pinpoint where it may be. You would have to start testing for voltage at the keys comparing working keys with non working keys and work backwards to the control board until you find where the problem is