Thanks for the info, brad808. Just to be clear, will doing this mean the JPAC will just directly pass-through any sync signal it gets? Bit worried about passing the 31khz signal to my arcade monitor at boot up.
Can I ask why you made this mod to your JPAC? Were you having the same sync issue as me?
Yes it'll pass everything through. Don't be worried about sending a boot signal for the few seconds before windows drivers kick in, or install atom bios to card.
Yes I had problems with J-pac sync circuit, I've had 5 now and all exhibit the same behavior so now I do this mod before I even install them. The sync circuit can't swap between 15-24-15 repeatedly for multisync monitors and needs to power down in order to regain sync. This is a big problem while using groovymame with auto sync monitors.
Also I've had in the past many times j-pac "randomly" drops sync of a signal it is displaying perfectly fine before. I wrote andy about this and he mentioned some people have had issues with the sync circuit not being able to properly identify certain modelines based on the sync pulse width being too narrow.
It was a problem that plagued my systems for a couple of years before I discovered this will solve it and not a single problem since.
If you want to test the jpac as well next time it happens, unplug the usb and plug it back in, see if it regains sync.