/diy/ - Do It Yourself

sup /ohm/, not sure if this is you or /mcg/, here goes.

I have a CZ-101 keyboard that has gone full retard since the last time I turned it on (weeks ago). All the front panel LEDs are intermittently flickering and the thing is no longer booting up as it should. It uses an NEC 7811G-120 CPU and an MB83256 mask ROM with a custom LSI toe generator.

Per the service manual all LEDs are driven by four LB1272 LED drivers, data is shifted in from the CPU via four 74HC374 flip flop arrays. While I do not have a logic analyser on hand I can see that the signal to each of the clock pins is "tripping up" in time with the flickering of the LEDs. Clocks and reset lines across the board are as they should be, the keyboard matrix sections are sending their data but nothing is sending to the tone chip. I have an ugly feeling the CPU or ROM has shat the bed.

I'm pretty sure this thing is now a door stop, though I'm considering a new old stock 7811G just for shiggles. $20 on fleabay, a pretty cheap hail mary. I may also be looking at a corrupted ROM, in which case this thing is deffo a boat anchor, I have no idea where I would get a copy of the firmware. I don't know how prone to failure Mask ROM is though, as compared to an EPROM for example.

Does anyone have a broad idea or can point me to resources on how I could further test the ROM or CPU? I have been considering trying to dump the ROM (too see if it actually works for starters and to hopefully get a copy of the firmware) but I'm not even sure where to begin on further testing.