Switch Matrix electronics knowledge needed

edelgiud

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OK, I posted in this section because it's not arcade related. I have an electronic music device where a sequencer start button that doesn't always start. Seems intermittent. If I twist the board, it is on it then works, but then later stops working. I think there is some sort of internal trace that's cracked, but I cannot find it under bright light behind the PCB. There seems to be no cold solder joints visible under lens either.
Can someone explain to me how this switch matrix works?
The button in question is the one that says R/S there at the top in the fourth column second row with SW6 pin 41.

I'm trying to understand if I can jumper a wire from one of the two pins of the switch, but I don't know if I have to jumper to one to ground or somewhere else. I think I understand that when I press the switch it essentially lets in the main CN10 pin SW6 to the main CN6 pin SW SC 3.

Maybe someone can help with their schematic reading knowledge. Thanks.
 

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Looks a lot like a pinball switch matrix. I think you're on the right track... closing that switch completes a circuit between the two connector pins you mentioned. None of the switches in the matrix should connect directly to ground.

Each switch also has a diode in series with it. Rather than show every diode, they have an inset at top left to let you know that each circle in the diagram contains a momentary switch and diode in the same arrangement.

As for your intermittent issue... hard to say without seeing the thing in person. Look close at the connections for the switch itself, the diode, as well as the switches and diodes that neighbor it in the matrix.

The good part of a matrix design is: more switches with fewer components, so lower cost and more compact PCB. The bad part is: troubleshooting can be more challenging.
 
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