IBM 5155 analogue display fault

[Tony Duell]

> Way ahead of you there - I've dismantled it sufficiently to at least
> check it's not something obvious. Like you say though, connecting the
> CGA output to a known-good monitor's probably the next step in order to
> see whether it's a display fault or a logic problem. The screen

Exactly. You don't want to spend time looking for a fault in the wrong place!

> appearance makes it look more like it's on the display side of things,
> but there's no guarantee at the moment.
> 
> (incidentally there are signs that it tries to boot, it gets annoyed and
> beeps if the keyboard isn't plugged in etc., so it looks like most of
> the digital side of things is happy at the very least.)

There's a bit of circuitry on the output side of the CGA card that can't 
be checked by the POST, 

> 
> > From what I remmeber, it's assembled with Bristol 
> > Spline screws, with the odd tamperproof Torx in the PSU. The former are 
> > not easy to get drivers for, I have a set, but they weren't cheap. 
> 
> Oh heck, yes. I went through every alan key and torx bit I had trying to
> find something that would fit the former. Ended up with a good ol' pair
> of long-nosed pliers, and those bristol spline screws are getting
> replaced with something a little more conventional on reassembly!

NO!! Those screws are part of the machine and should be kept. I feel very 
strongly about keeping odd fasteners, etc in machines, to replace them 
with anything else does change the character of the machine IMHO. Surely 
you can buy a set of Bristol Spline keys (I think Farnell do them...)

-tony