Electronics > Repair
Pinball CPU data lines pulled up to 1.2V
Ian.M:
That depends on what its connected to. The address lines probably only go to the CPU, RAM, ROM and PAL, as if you have a PAL for address decoding why would you also use a mess of TTL MSI logic for that function? The odds are there are some TTL latches for output and tristate buffers for input, connected to the data bus and their addressing controlled by the PAL.
floobydust:
Is it the MPU board for The Lost World Jurassic Park pinball machine?
Which schematic do you have? I found one but too low rez scan.
drhex:
Good quality schematic is here: https://pinwiki.com/wiki/images/e/ec/CPU_Sound_Bd.pdf
A few pics attached, two of the data lines, one of the address bus
Data:
Address:
Data really looks wonky to me.
This board was used in plenty of machines, currently has X-Files ROMs on it (which I read out, they are good). Doesn't initiate things properly, PRES is always held high e.g. so the display is never initialized. It is running though as per the images, just probably not the right stuff. The guy owning the corresponding pinball said it went all crazy when testing. Found a short between two data lines in the first go which got LED200 lit - this is the only debug info the board creates. I also took out U206 as that was leaking through the voltages from the noise supressing caps/pull ups - this cleaned up things considerably. I don't know the history of the board, it was sold as defective on the Bay apparently. Could well be that someone took 50V coil power into it. Also, there is some battery leakage damage, sockets were replaced by the owner (this is where I found a short) and some corroded traces repaired.
floobydust:
Those waveforms are the databus with the CPU U209, SRAM, EEPROM removed? Not the plasma controller databus, not the BSMT2000 databus? I see a mix of 'LS and CMOS logic.
Strange to see some clock modulated? signals there. I suspect the PAL16V8Q might have internal pullups and it should not be enabling anything if the address bus is dead off. But somebody drives it to 5V once in a while. Who is that?
drhex:
No, everything in, three logic chips powered off. U5, U206, U208. This is straight from pins 23, 24 and 25 on the CPU. Also, I think everything on that bus is LS or HC, so should be 5V?
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