SWTPC 6800 weirdness

Brad H vintagecomputer at bettercomputing.net
Tue Sep 6 15:58:31 CDT 2016

-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Fred Cisin
Sent: Tuesday, September 6, 2016 11:36 AM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Subject: Re: SWTPC 6800 weirdness

On Tue, 6 Sep 2016, Brad H wrote:
> My 6800 has been mostly working, but it seems to be occasionally 
> flaking out.  I don't know why.  Sometimes you go to power it up, and 
> there's no response on terminal side.  The 'fix' is sometimes to 
> wiggle the memory/CPU boards and then for some reason it's fine(ish).  
> There are five cards

fix by wiggling implies a bad connection.
possibly due to oxidation or corrosion of connector?
Depending on how vigorous the wiggling is, it could even be bad connection
between a chip and socket, or even tiny damage to a trace on the board.

> Today it flaked again and would not come back up, so I pulled the MP-M 
> board and the MP-A board and swapped slots.  It came up, but memory at
$0100 was
> missing.    I tried powering up, swapping slots, etc.. same deal.  Then I
> left the machine for an hour, powered up again.. boom.. now $0100 is back.

>Working later could be a thermal problem, or just random chance.

There is definitely some oxidation around the board and on some pins, which
I thought I cleaned well enough on the particular slots I'm using.  I'll
check again.  It seems odd that mechanical fooling around makes it work.
Could be totally coincidental though.  I've been a bit hesitant about taking
the board out as I worry about fragility.. but I think we're past that now.

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