28 Nov
2016
28 Nov
'16
10:56 p.m.
On November 28, 2016 1:37:54 PM CST, "Ian S. King" <isking at uw.edu>
wrote:
On Mon, Nov 28, 2016 at 8:22 AM, Brad H
<vintagecomputer at bettercomputing.net
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
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