G’day from Sydney Australia, Synth wizards!
Hoping someone can help me with a main board problem on my Roland Jx-3p!
It appeared to be quite dead but after checking voltages and signals on the main board with my scope I can see quite a bit of activity. None of the LEDs are lit and it doesn’t respond to buttons or keypresses. Power supply is working the main board has +5v, +15v and -15v as expected. The CPU reset, RAM reset, CPU clock and ALE all working and the address bus is very busy. What I notice is that the logic used to scan the keyboard & panel or drive the LEDs requires the CPU to toggle the WR and RD lines (pins 16 and 17) but they both stay high. I haven’t seen either line switch LOW. I can see some of the other logic working; for example the I/O decoder chip (IC41) is cycling through Y1-9, so it appears to be attempting to read the panel switches & keys but IC40 needs the CPU RD line to be set low to gate the signal. CPU RD doesn’t change at all. In the hope that the CPU RD & WR lines were being pulled high by something external to the CPU I replaced IC 30, 40 and 53 but no change.
The only other chips that use the RD / WR lines are the static RAM (TC5517APL and the 8031 itself). I’ve ordered both chips so my next step will be to replace one or both…but…I’m hoping there might be something I’ve missed…?
Could there be another reason why the 8031 would hold the READ and WRITE lines both high…? - it seems inconsistent to have them both at the same logic level as it can’t do both at the same time?
