Vintage Synth Explorer Forums

Hi all, I've got a very sick Jupiter 6 that a previous owner installed the Europa mod in. I suspect something is wrong with the CPU and would like to turn the board to stock to rule out the mod as the fault.

I have already ordered a couple 8031's from Jameco but I understand that I will also have to burn the EEPROM with the original OS. This is uncharted territory for me and any help is appreciated, is the EEPROM that needs rewriting the chip next to the 40pin cpu or is this internal EEPROM being referenced?

Also, can anyone recommend an inexpensive EEPROM programmer?

If you're curious about the fault I'm trying to repair I've made a demo video showing the synth in its faulty state, after a few reboots it starts working as expected. (For a few minutes anyway)

Have you put a scope on the power lines? I would definitely check those before doing what you mentioned. To me, this looks like the synth is having trouble achieving a stable 5V, so the unit is going in and out of RESET.
-Rob
www.newenglandanalog.com

Hey neanalog, I have put a scope on the PSU lines as well as the RESET line from the PSU and at TP3 on the CPU board. As far as I can tell everything looks okay.

Reset signal:

-Yellow = TP3 on CPU board
-Blue = RST on PSU board

I'm not sure if that little bump on the leading edge of the reset signal is an issue or not but sometimes it is worse than others. (In the automotive world something like that would be worth investigating but it doesn't seem too critical in this application) The service manual does indicate that the duration of the reset should be ~80ms from start to end, mine is consistently around 50ms. (Again, not sure if this is an issue or not since it seems to work okay occasionally.)

5v rail:


I have ordered a set of EPROM modules from ebay and the 8031 CPU's came in last week. I haven't been able to find any evidence to nail down an issue on the PSU or CPU side but I'm starting to run out of ideas. I have removed and cleaned all of the connectors between the CPU and Module boards and that seems to have resolved the crackling glitchy audio, for now at least. Now though, 4 out of 5 times the board will not boot when powered on. Sometimes the Europa OS will report no response from the modules boards, other times I get no lights at all..