You were spot on. Seems like it reads the final drop down voltage on those button tracks. i got 3 'outputs' from those buttons, 2 goes to pins on a ribbon cable that goes to a logic board... another one is giving me some more trouble.
KEY0 and KEY1 output pins each handle 8 buttons and vary from
I measured all those going from the +5VL pin (from the power board) to the respective KEY0 and KEY1 that goes to a logic board, (btw what is VL? ...it sits right next to one called +5VD), [o]but KEY2 do not seem to go to any logic board, but instead goes back to the power board ...
ah, ok, gotcha. the other question was why only this rail has the resistence ranges all in the >1K Ohm... it's because the last button on this chain is the power button. with 0Ohms. So i think i solved the mistery... just let me know if i'm way off here:
the KEY2 is like the ATX power button in computers... it's "always live" and anything <1Kohm will trigger a power on.
So KEY2 last button is power, which has 0ohm, pressing it powers on the board. after it's on, it probably forwards the pulldown information from the remaining 5 buttons on the track (1k, 2.5k, 4.5k, 7k, 12k) to the logic board somewhere on the power board... probably including the power button so the logic board decides how/when to put it back into stand by or something.
Ok, so if that's correct, all that's missing is VL vs VD? is this something standard? or is it something particular to this setup (i'd imagine Voltage Live, Voltage Dead or something
that's what i get for doing stuff in the interval of a game... that's all wrong
. as soon as i tested with the daugher board attached i was able to get a KEY2 output matching exactly the same impendances as KEY0 and KE1 for the key2 buttons. it messed me up a little because for the daugther board signals there's a key2+ and key2- pins, but of course, when you attach the damn thing it closes the loop and now it's all the KEY2 rail. so it's pretty much powering the logic board at all times and it decides when the power button was pressed or not. nothing like ATX here... also there's two buttons i missed on the other side, so it's all 8 buttons with the very same values distributed.