I have 4 PC Chips M507 boards (two dead). They have JP4 jumper which is not documented anywhere. The only thing that's printed on the board is "JP4: IRQ". It's between the ROM and RTC, consists of 5 two-pin jumpers. They were all open on all 4 boards. Using ohm-meter, found out that the upper pins are connected to IRQ lines (5, 14, 10, 14 and 12). I guess that it's IRQ selection for something. But for WHAT
Weird thing: the bottom pins are NOT connected together
