SWTPC 6800 issues again
Ian S. King
isking at uw.edu
Mon Nov 28 13:37:54 CST 2016
On Mon, Nov 28, 2016 at 8:22 AM, Brad H <vintagecomputer at bettercomputing.net
> 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.
> wasn't sure how to properly test the $A000 board - I assumed I couldn't
> the test test the address space used by the test program itself, so I set
> to run from A07F to AFFF (I think I did that right, I set the MSB in A002
> A0 and LSB in A003 to 7F, and for the upper limit MSB in A004 to AF and
> 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.
> do you think on that?
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
Ian S. King, MSIS, MSCS, Ph.D. Candidate
The Information School <http://ischool.uw.edu>
Dissertation: "Why the Conversation Mattered: Constructing a Sociotechnical
Narrative Through a Design Lens
Archivist, Voices From the Rwanda Tribunal <http://tribunalvoices.org>
Value Sensitive Design Research Lab <http://vsdesign.org>
University of Washington
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