I've got another japanese Esprade and this one have another kind of issue. What's wrong with these boards ?
The service switch seems to be always on. I'm not talking about the test switch on the board. When I switch the cab on, I don't even have the time to read the warning screen with the "Use in japan only" writting. It goes directly to the title screen with 1 credit insered already. I can't add any additionnal credit nor start a new game when I get a game over. I have to switch the cab off for that. I've checked the board and I don't see anything suspicious, it looks brand new. I've tried many other boards on this cab and I know for sure that the problem don't comes from it.
Try it in another cab. Some Cave games behave oddly when credit buttons are held down, but most boards don't give a damn.
If it still does it, sounds like you have a stuck input. You'll need to work out if it's actually the service button it thinks is held, or coin 1/2 - they'd all cause the same thing I think. Then trace the track and see what chips and/or resistor arrays it goes to. You might get lucky and find some pins are touching on the underside, if that was the cause it would likely be near the edge connector. If not, you're definitely in PCB repair territory.
Thank you for the help bloodflowers, I'll look into it. Btw, I know for sure that it's not the cab because I've played 3 different Esprade PCBs on it without any trouble.
Look for 74LS245s or 74LS253s around the dipswitches (this advice isnt specific to that board, just both common chips used to read the dipswitch settings into the system- they will be close to the dips, they are common chips elsewhere on boards so if they aint close they are not going to be relevant). If they are Fujitsu brand then suspect them even more.
Set your multimeter to continuity buzzer and buzz through from the dipswitch leg for the relevant switch to the legs on the above chips to find which one is relevant, if you have a logic probe ($20) you can check whether the output for that chip input is stuck or not.
Also possible that the dipswitch is just drity inside, worth flipping it a dozen times or so to try and wake it up.
Thank you very much Womble but there is no dip swithes on this PCB, only a test button to acces the game menu. I've found a Motorola 74LS245N though, not sure if it is one of those chip that you're talking about ?
