When taking new screenshots for my old PC-FX articles, I noticed that my PC-FX mouse (FX-MOU) didn’t work properly anymore. It still detected the movement fine, but if failed to register one of the mouse buttons. My spare mouse turned out to suffer from this too.
It’s time for a quick repair. Two screws underneath the label hold the mouse together (marked with yellow circles).
NEC PC-FX Mouse (FX-MOU) – inside
The PCB is labelled Mitsumi TD-T13V.
NEC PC-FX Mouse (FX-MOU) – PCB 
The buttons are labelled Omrom B3M, which points to the replacement part: Omron B3M-6009 long-stroke tactile switch.
A final test with the new buttons before closing the mouse: The mouse works fine again and the click sound is much louder than before.
The PCB of the second mouse has a subtle difference: The four solder jumpers 1-4 are open. Upon closer inspection, we can see on the back that the jumpers switch the resistors of the light emitters/detectors of the encoders in parallel.
NEC PC-FX Mouse (FX-MOU) – PCB #2 
I didn’t investigate this difference any further though because both mice work fine as they are.
One thought on “NEC PC-FX Mouse (FX-MOU) Repair”