Perq 2T1 display fault

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Fri Feb 20 19:45:50 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
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.


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.
 
> 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.

> The only non-standard feature is
> the monitor power cable -- I couldn't find the original lead, and the
> connector at the monitor end is something odd. So I removed that
> connector, fitted a length of cable with a 3 pin DIN plug (to fit the
> PERQ's 55V output socket) and wired the other end inside the monitor,
> using a strain-relief bush in the holw where the power connector used to
> be. That shouldn't cause many problems.

That's definitely the machine. I remember thinking it odd that all the
cables from the monitor were socketed apart from the power lead :)

> one), the vertical osciallator components, and the vertical output stage
> comopnents. The latter 2 connect to presets and a TDA1170 chip. AFAIK,
> the circuitry is conventional.

I think I mentioned in the original post that, IIRC, those same chips
are used in Cub monitors and have a habit of cooking themselves. Pretty
sure they tend to result in just a single hoizontal line in the centre
of the screen when they go though, not 'missing' lines as I'm seeing.

> Do you have an EHT voltmeter?

Personally, no. I'll hunt around in the museum for one tomorrow (I'm
sure some of the radio room or Colossus guys must have one)


> > (there is a PERQ 1 also with a video fault which I think I mentioned;
> > that's where the confusion probably arises. That one has a totally
> > mangled display, squashed horizontally and vertically, very non-linear,
> > and no recognisable character output on it at all)
>
> Do you _know_ if the PERQ is giving the right scan frequencies? (64kHz
> horizontal, 60Hz vertical IIRC).

No idea on that one unfortunately - that why I thought I'd worry about
the 2T1 first as it at least looks like it's trying to do something
useful :)

cheers

Jules
Received on Fri Feb 20 2004 - 19:45:50 GMT