Yamaha PSR 225 keyboard pcb board

Thread Starter

bo_9

Joined Feb 6, 2020
1
this Yamaha psr 225gm digital keyboard has a set of keys that do not work. all the keys that do not work are along 2 circuits that then connect to the microprocessor. On the. Board that has the microprocessor where all the key matrix circuit lines come together it seems Like there is some sort of short happening. If I test for continuity on different pins there is some response from pins that don’t seem to be on the same circuit. But I’m not sure how that could be. They are connected along what I think is a capacitor although I’m not entirely sure about that because it doesn’t look like any capacitor I’ve seen. It’s the one labeled c101m In the first photo and the long row of pins above the microprocessor that my fingers shadow is pointed at. these pins have some continuity between themselves that is strongest on pins near each other that fades out as I test pins further from each other. So is It possible for the mystery component/ possible capacitor to go bad and allow this to happen? Or is it possibly something wrong with the microprocessor? I am not very experienced with circuits but its my friends keyboard and she can’t afford to buy a new one right now. Any ideas, explanations, or corrections are welcome. image.jpg
 

Attachments

Dodgydave

Joined Jun 22, 2012
8,866
C101M will be a Resistor block, maybe 1K or 100R, with a common pin to ground, it's probably a pull down block, and the keys put a positive pulse on the micro,. It's best to draw out the circuit around the keys, or search for the Service manual.
 
Last edited:

twohats

Joined Oct 28, 2015
97
I think the 101 indicates 100 ohms. Screenshot from RS Components (UK). Example only: Resistor Network 102 = 1000 ohms. You could use individual resistors, of the correct sort.
 

Attachments

Top