Taito Under fire 2nd player issue on board level?

[ferris129]

Hey! i am working on a Taito Under Fire arcade machine where everything seems to work except the second player gun, i have tried swapping the connecters on the board and this fixes the issue but makes the first player gun not work which tells me that its probably a board level issue and the controller itself is working fine? i tried finding out what parts could be causing such issues on this board but had little success so far. I have taken some measurements at the connector on the board but it seems like both ports are getting the same measurements on each of their pins when i compare player 1 and player 2, the cables also seem all fine on the board.. this had made me a little lost on where to check next since i cant find a good pcb plan online so far.. if someone has any idea what component to check or in what area it could be worth to check i would appreciate help a lot! my knowledge on arcades and crt is still very small sadly..

 

[ferris129]

small update..
I have taken out the pcb and checked all the soldering but it all looks quite good to me, the measurements also did not yield to much sadly but i am also not to certain what i should get as measurements, there are some test pins on the smaller top board but i would probably need an oscillator for this kind of testing i assume.. all components i could see seem visually okay and resistors have all the right values, the ferrite beads are also all fine as far as i can tell since they should just have continuity? i followed the traces too but they all seem to be intact according to my multimeter.. i am almost wondering if there is some kind of software related lock that limits it to 1 player or such^^

 

[BigP_BigP]

Probably a logic probe is enough. Start working your way back from the connector checking for continuity and component values with the board off, sometimes a broken trace or joint is not visible. Then once you hit logic, probe with the board on to check for stuck logic outputs/inputs.