Syscheck Troubleshooting

[hueyjones70]

Syscheck indicates that my 800XL has a bad dram at location U9. Replacing U9 has no effect. I have replaced every IC on the board and nothing has changed. I believe this indicates a short; if so, where should I start looking. I replaced the socket at U9 and didn't see anything wrong there.

[Beeblebrox]

Could be a short but syscheck has been known to throw up false dram errors when other faults are present as far as I recall. I seem to remember a failing rom was causing a bad ram diagnosis at one stage when I was using it.  And visa versa. IIRC I replaced the rom and the ram errors no longer showed. It's been a while. Sys check ii is an amazing device and in the past it has saved me many hours whilst troubleshooting. 

 

 

 

 

[xrbrevin]

is yours an 800XLF? i think they have diff'rent IC numbers

[hueyjones70]

It isn't an XLF, and I changed the ROM, MMU, and every other IC on the PCB.

[+scorpio_ny]

Maybe check to make sure that there are no bad connection with memory socket with the PCB? I had a perfectly working 800XL that went bad out of the blue. After two weeks of checking, I discovered that one of the pins of the OS ROM socket had a bad solder joint that may have broke due to the PCB flexing. After a solder reflow, it was back in action.