80286 Protected Mode Test

[Rob Jarratt]

I should update people on this as I have made progress today. I found two
broken tracks from the 8742 peripheral controller to the ASICs. One of the
ASICs sends a RESET to the 286. When I repaired that track suddenly the
protected mode test started to pass. Now I have other errors which are
almost certainly other bad tracks, although these errors are more
intermittent so it could be a track that is partially damaged.

Regards

Rob

> -----Original Message-----
> From: Rob Jarratt <robert.jarratt at ntlworld.com>
> Sent: 06 March 2021 23:30
> To: 'Richard Pope' <mechanic_2 at charter.net>; rob at jarratt.me.uk; 'General
> Discussion: On-Topic and Off-Topic Posts' <cctalk at classiccmp.org>
> Subject: RE: 80286 Protected Mode Test
> 
> 
> > -----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
> follow
> > 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.
> 
> Thanks
> 
> Rob
> 
> > 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
> > >
> > >