SWTPC 6800 issues again - test-drb@ccmp.vtda.org

28 Nov 2016

It tested good with my DVM when I first had it.. but the cap is original for sure... maybe
I will invest in a new one even though it seemed ok.

Sent from my Samsung device

-------- Original message --------
From: "Ian S. King" <isking at uw.edu> 
Date: 2016-11-28  11:37 AM  (GMT-08:00) 
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org> 
Subject: Re: SWTPC 6800 issues again 

On Mon, Nov 28, 2016 at 8:22 AM, Brad H <vintagecomputer at bettercomputing.net
...
  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

-- 
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

There is an old Vulcan saying: "Only Nixon could go to China."