PC Chips M507 - what's JP4 for?

[Rainbow]

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

[Rainbow]

No IRQ selection. Ohm-meter shows that all pins are IRQ lines. Looks like this is not a jumper field but a connector for some kind of diagnostic device.
Pinout:

Code: Select all

All numbers are IRQs

5  14 10 4  12
.  .  .  .  .
.  .  .  .  .
6  7  15 3  11