Fun with a DWUBA

--- Gunther Schadow <gunther(a)aurora.regenstrief.org> wrote: OK... moving right along, I have checked everything out step by step and a) nothing smoked :-) , but b) nothing worked. :-( According to the docs, when I read the general purpose register at 200000f0, it tells me that the card failed test 3 which is an internal RAM test. I swapped gate arrays with the other card (socketed) and there was no change in the test behavior. Not surprising, really; the original fault seems to have roached both boards, so the same parts are at risk. Only one PCB was damaged, so that's fortunate. There's something deeper wrong with this board that simple visual inspection does not reveal. Nope... I did a systematic test and had it all plugged in and not smoking earlier tonight. I started by ensuring I knew which pin on the Unibus cable and paddle card was connected to the fried trace - it was Unibus pin AU2 - one of the grant signals. I checked for wierd voltages at the T1010 end with the BA-11 powered on - nothing. Next, I checked for direct shorts to ground. Nope. I then powered up the BA-11 and not the BA-32 (well... the BA-32 was in standby which activates the DEC power bus to turn on the BA-11) with all cables and boards in place - monitoring the affected pin showed TTL-compatible voltages (between 1.8 and 3.5VDC). Finally, I did a quick on-check-off test... no odd readings on AU2. I inspected the board, no warmth where there had been problems before. I did a longer on-check-off test and verified that I still got no yellow LED and a "-0" on the BI POST. Board still did not show odd warmness. I stepped through the diagnostic procedure in the DWBUA Technical Manual for the section that covers "light does not come on". It was there that it mentioned checking the base address + F0 (a BIIC register that is available for any use the module designer sees fit - there are 4 total; we used one in the COMBOARD-BI as the "window" register we implemented in hardware ourselves with previous COMBOARD designs). In the case of the DWBUA, it is a status register that indicates if the Unibus is powered up or not, and what the results of the selftest were. Since I read a 00030081, it tells me that test "03" was where it failed, and the rest of the register is undefined (it should read 00000001 when all is well - Unibus powered up, no snags with the diagnostics). Cool. I think I do. Looks like I have either an address fault or a data fault with the "IRAM" on the card. Could be a RAM chip, could be a logic chip. None of that stuff is socketed except a PAL or two. At least I can drop it in my box without fear of letting out the smoke. I wish I knew why the previous ones smoked. Perhaps the cable got crimped. Perhaps I was using a different M9313 card on the bus and that one had a short to ground on AU2 (I have more than 4 UETs and I don't know which one was in the BA-11 8 years ago). -ethan __________________________________________________ Do You Yahoo!? Yahoo! Sports - live college hoops coverage http://sports.yahoo.com/