80286 Protected Mode Test

Rob Jarratt robert.jarratt at ntlworld.com
Sat Mar 6 17:29:54 CST 2021

> -----Original Message-----
> From: Richard Pope <mechanic_2 at charter.net>
> Sent: 06 March 2021 23:20
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Subject: Re: 80286 Protected Mode Test
> Rob,
>      There is probably hidden damage to the motherboard. The acid will
> the traces inside the board and consume them. There is no way to stop this
> kind of damage. Sorry for the bad news.

I should have said that I have found a few bad tracks and I have fixed them
by adding wires. Previously it would not even POST, but it does now. The CPU
is physically distant from the battery damage. I am trying to understand if
this particular test could fail due to external factors or not so that I can
then investigate if there are other tracks I need to fix.

Incidentally, my repair wires are done very badly, are there any tips on how
to do this well? I have ordered some wire wrap wire because I believe that
is what I should be using, but I haven't got the wire yet.



> GOD Bless and Thanks,
> rich!
> On 3/6/2021 4:59 PM, Rob Jarratt via cctalk wrote:
> > I have a DECstation 220 (Olivetti M250E) which is failing POST on a
> > "simple test of the 80286 protected mode". It says in a service manual
> > I have that for this test the CPU is set in the protected mode, the
> > machine status word is checked to see whether it indicates the
> > protected mode and then exits protected mode. This test seems to be
> > failing. Is there any possible explanation for this other than a
> > failed 80286 CPU? Could there be any external reason? This board
> > suffered some battery leak damage. Clearly the
> > 80286 is working well enough to execute this diagnostic and send some
> > text to the screen, so it basically works.
> >
> >
> >
> > Thanks
> >
> >
> >
> > Rob
> >
> >

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