Roland JX-8P Locks Up after Booting - Erratic Behavior

Synth Repair
1

My 8P appears to boot (completes countdown), but then goes berserk and everything appears to be locked up (with no sound). Most of the time, the display flashes “Insert Cartridge,” but occasionally the panel LEDs will flash and there will be a few seconds of garbled ROM data flashing rapidly on the display. For a while I thought this behavior could be the result of panel switches being held active by a faulty IC, but I have not been able to prove this. Looking at the MIDI out, I occasionally see some CCs, but otherwise the note data is nonexistent. Based on my understanding of the system architecture, I am fairly certain that the fault only exists within the controller/programmer half of the mainboard.

I borrowed the mainboard from a known working 8P that seems to work fine when swapped in this chassis, so the power supply, display, and panel boards should all be good. I tested the traces connecting ICs and connectors. I also swapped ROMs, replaced CPU and RAM just to confirm that those were good. I probed all of the pins on the suspect ICs between both boards and the only major difference I noticed was that the CPU was being sent a 32kHz interrupt signal on the bad board.

At this point, I’ve tested every IC in the vicinity of the panel switch driver circuit and CPU/data bus the with my tester. All of them tested OK, although I’m really not sure how thorough my tester is. The only IC I have no way of testing is the Roland gate array (IC2), but otherwise I have run out of ideas and things to test.

Any suggestions? This is not my first synth repair rodeo, but I’m really stumped on this one…

1 Like
2

It sounds like you’re on the track with that interrupt signal.

Which CPU are you looking at? I see that the HD63B03 has IRQ going to the gate array, but the NMI is running off to the 8051 CPU. There’s an interrupt on the 8051 that seems to be connecting into a counter.

2 Likes
3

ProfTrudo, thanks for the reply. I assume the NMI signal is active low? It looks like the NMI between the 8051 and the hitachi assigner CPU is always held at ~5v on both boards, so I don’t think the Synth side of the mainboard is causing the problem.

4

I’m looking at a poor pdf copy of the service manual, so it’s a bit of a chore to figure out what’s going on with this synth. And I don’t have a JX-8P to reference.

I gather that the HD63B03RP is responsible for interpreting the key, MIDI IN, control panels, and cartridge, while the 8051 handles voice assignment and MIDI OUT.

Which line did you find the 32kHz signal?

According to the datasheet for the HD63B03RP, a low on pin 4 will cause the CPU to jump to the NMI routine. And a low on pin 5 will send it to the IRQ routine.

That IRQ line is coming from the gate array pin 28 starting from SN530350. That’s making me wonder about the board you swapped in.

As long as neither pins are held low, I think the processor should be running. Can you verify that the address and data lines are active when the keyboard is locked up? Clock signals?

How is the power supply? If a supply voltage goes low, it might force the cpu into a standby state. Are any of the chips getting too warm?