Perq 2T1 display fault

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Feb 20 21:48:09 2004

>
> On Fri, 2004-02-20 at 23:18, Tony Duell wrote:
> > > > Just to confirm, we're talking about a PERQ 1 here -- it's confusing to
> > > > me wether this is a PERQ 1 (verically-mounted SA4000 hard disk at the
> > > > left side, monito connects on a single DC37 connector) or a PERQ 2T1
> > >
> > > It's a 2T1, vertical drive mounted at the back.
> >
> > Oh, right...
> >
> > Can you please re-describe the 2 faults and the machines they occur on --
> > I was under the impression I was considering a PERQ 1 (VMI monitor) with
> > a small picture all round...
>
> Well the 2T1 is the one I'll try and sort out first, as that one
> certainly appears to have a healthy (or almost-healthy) system unit.
>
> So, the 2T1 has a standard KME as you say - it looks to have correct
> horizontal and vertical drive, with the exception that it skips every
> few lines, leaving a blank horizontal gap. I can see what look to be

That does _not_ sound like a monitor problem. You're getting missing
video every few scan lines, right? In which case, either you've got some
Analogue signal that's blanking the display _and_ which is locked to the
vertcial sync signal, or you've got a problem with the memory board
(middle board in the cardcage) in the PERQ.

How far does it get through the self-tests? What's the final number on
the DDS display (front of the CPU box) when it tries to boot?


> characters on the display, but they're not at all readable. Difficult to
> tell if it's scrambled pixels (suggesting a system fault) or an analogue
> problem (suggesting the monitor). The display has an unstable shimmering
> right margin to it, which definitely looks analogue in nature.

That may be normal. There's some marginal timing in the vidro circuitry,
and often the right few pixels are a bit unstable :-( At least one of my
PERQs does that...

>
>
> Onto the PERQ 1. Standard monitor as you say - only that one is
> *totally* stuffed. The picture (such as it is) is collapsed into maybe
> 2" vertically, and about 80% of the screen width horizontally. It's
> extremely non-linear; left and right margins weave all over the place. I
> can see beam traces all over the shop within the squashed picture too.
> It's actually quite a work of art! Not sure if there's more than one
> fault going on here, or whether some critical point isn't getting to the
> right voltage and that's causing the whole thing to fail.

I will ook at the VMI manuals... This one does sound to have some kind of
monitor problem...

>
> > OK, back to the T1. I think it's the machine I worked on some years ago
> > (don't worry, everything is 'stock', apart from the fact you may find the
> > odd IC in a socket if I replaced it).
>
> Ahh, yes it will be. I checked all the connectors and reseated the
> boards plus chips - I remember seeing a few socketed ones that didn't
> look like they would have originally been socketed.

You'd be suprised. The only chips I _remember_ socketting was an op-amp
on the hard disk analogue PCB.

Origianlly, all programmed devices (PROMS, PALs, the EPROM on the EIO
board) were socketed. So where some of the I/O devices on the EIO board.
And a fair number of control logic chips on the memory board may be
socketed, espeically if there are kludgewires soldered to them...

-tony
Received on Fri Feb 20 2004 - 21:48:09 GMT