On November 28, 2016 1:37:54 PM CST, "Ian S. King" <[email protected]> wrote: >On Mon, Nov 28, 2016 at 8:22 AM, Brad H ><[email protected] >> wrote: > >> Hey guys, >> >> >> >> You might recall a while back I was having issues where I'd have to >power >> up/power off multiple times before I'd get the 6800 to start up >correctly >> and give me the SWTBUG prompt. What I did was remove an overwrought >> modified RAM board and replaced it with a more basic 4K board set to >the >> $A000 range. That worked great for a while, but not we're getting >back to >> the situation where I power up many times and get either ? marks, a >string >> of 4s, or some other random character. I have to power off and on >several >> times before I get the $ prompt. >> >> >> >> I figured out how to run a proper RAM diagnostic and no errors came >back. >> I >> wasn't sure how to properly test the $A000 board - I assumed I >couldn't >> let >> the test test the address space used by the test program itself, so I >set >> it >> to run from A07F to AFFF (I think I did that right, I set the MSB in >A002 >> to >> A0 and LSB in A003 to 7F, and for the upper limit MSB in A004 to AF >and >> A005 >> to FF). >> >> >> >> I'm wondering now if this is really a RAM problem or maybe something >else. >> I don't think it's the serial card.. I've tried both the MP-C and >MP-S and >> no change. >> >> >> >> I have an NOS MP-B2 motherboard here. The 'check pins' on the molex >> connectors for the cards haven't even been cut. I could set that up >for >> testing although, being totally unused I'm hesitant about altering >it. >> What >> do you think on that? >> >> >> >> Brad >> >> >My first question (and pardon me if this was addressed in your earlier >thread) is, have you checked the power supply? If possible, use a >scope, >but even a good DVM will tell you if you're maintaining voltage. And >if >the filter cap is the original, just replace it - they have a limited >lifespan. I bought one from Digi-Key for $19. Hope that helps -- Ian
Also, confirm that the connector on the power supply board (next to the big cap Ian references), that leads off to the motherboard, still has nice clean *unburned* pins. Those Molex pins were marginal at best for a heavily loaded backplane and I found mine had been heating and were pretty much toast. This results in huge drop of the +8V before it gets to the motherboard even if it looks all nice and happy across that big filter cap. Chris -- Chris Elmquist
