well, just an update for anyone who cares:
I did eventually get some good advice from some people over on the synth DIY subreddit.
one person told me I needed to wire a diode in series before connecting to the keyboard matrix, but we eventually determined that this wasn’t the case, as only the “n” column pins in the matrix have diodes, and not the “s” pins (the rows), which would be the ones containing these secret drum samples.
Then I received a great reply with the actual probable answer; all of these pins connected to the matrix are also connected to “pull-up” resistors. Before this project & reply, I had never even heard of pull-up or pull-down resistors, logic states, or any of that. But basically, the reason this hadn’t worked previously, is because this pin should be “active-high”, and needs to be connected to VCC via a 4.7k resistor like all of its neighboring pins to work properly.
Well, sadly, I tried this and still, no results. So at this point, ive decided to throw in the towel. It’s possible that even with the probably-correct solution in front of me, I still managed to wire it up incorrectly, and that’s why this didn’t work. It’s also possible that there was simply a software change on this chip between the PSS-80 & the PSS-125, and no amount of fiddling will ever unlock this drum pad ive spent so much time chasing. Honestly, who knows? Maybe someone will come along and succeed where i’ve failed one day, but for now, the PSS-80 remains drumpad-less.
Except… There actually IS a drum pad on the PSS-80, though its not super practical to use. By booting into its secret test mode (holding 2 highest keys while powering on), you not only reroute all of the face buttons to the keyboard, but you also turn the “voice select” buttons into a real, working drum pad.
The only issue; Because all of the buttons are rerouted, all of the keyboards usual functions are disabled with test mode enabled. And they stay disabled, until you turn the machine off and back on again, disabling the drum pad. Ive done lots of experimenting with this test mode to try to unlock aspects of it in normal boot up mode (it also has a cool reverb voice only accessible during normal operation) and re-route these drum buttons, but I haven’t had any luck there either.
Funny how a functioning drum pad on this device always seems to be so tantalizingly close in so many ways, but also completely unachievable 😭
Anyway. Thats where I leave this project. Maybe someone will pick up this torch some day and continue on, but for me, it’s the end of the road ✌🏼