Ok i had time to poke around.
JP1-6 and 8-11 have no connection on pin 1; and are connected to gnd via 10k resistors.
They only have an effect when i put them directly to gnd (1k also works).
JP7 and 12-15 are IRQ jumpers (LPT/COM) and go to the chip and irq-buslanes, without resistors.
- COM A/B enable/disable
- COM adress
- LPT enable/disbale
- LPT Bidirectional/Output
are going to the controller chip and further to this "HM8388P" dip20.
4. Jumper 6 "LPT Port"
pin 1 : not connected
pin3 : resistor -> gnd
pin2: controller chip -> cap (c4) -> gameport -> gnd
5. Strange gameport, what are 10pin gameports doing on PCs.
6. HMC HM8388P
I couldn't find a datasheet.
1 : 12v
2-7: COM/LPT as descibed in 3.
2-7: 5V... or when i pull them directly to ground (not going through the 10k resistors) change to 0V.
14-19: changing between -12/+12V depending on enabled/disabled COM-ports.
Some more things:
I got curious and pulled out the diodes through which the +-12V are going.
- The -12V side goes dark
- The +12V side gets from pin 2-7 5V.
So it seems the 5V for the defined state is originating at the controller chip.
Anyways what could be defective so that the jumpers have no effect. I mean it can't be a design mistake, or could it be that the wanted to put in 1k resistor and mistakenly got 10k ones?
Greetings and good night!