One of the guns on a Time Crisis 2 was no longer registering shots on the screen.
Following checks on wiring, cleaning lens, etc. it appeared that the optical sensor (opto) was dead. This is a small PCB in the gun, 2421961100, pictured above.
I couldn’t find any schematics or information about the parts used, and replacement PCBs, where available were quite expensive.
I did find a comment on a forum about the guns provided for use with a PS1 based Konami gun game – “I am very happy to come back with a definitive answer to this lingering problem. A 100 percent tested and compatible drop in replacement is the IS485E”
They also provided a photo of the sensor board, and apart from the addition of a capacitor it looked very similar to the Namco PCB.
I ordered some from a Chinese website (10 for about £7.50) and duly waited for them to arrive.
Fitting required the central pin (which is bent forward on the optical sensors I received) bending so it was facing the opposite direction. You also need to mount this so that the top of the sensor it 7mm from the PCB. (so it fits in the notch on the gun)
End result – the gun now works as expected.