IBM 5155 analogue display fault

[Tony Duell]

> > That is not an excuse. Anyone working on IBM 5155s (or for that matter=20
> > Friden Flexowriters, which are stuffed with setscrews needing Bristol=20
> > Spline drivers) should have a set.=20
> 
> Are they the ones that are the same shape as a tractor PTO shaft?

Roughly, yes (although I've never worked on a Tractor...). I think of 
them as : 

Allen : Triangular wave rapped round a circle
Torx : Sine wave rapped round a circle
Bristol : Square wave wrapped round a circle

Very approximate, of course (and certainly not enough to machine a tool 
to fit them), but it gives the right idea.

> > or had been moodifed to allow a normal driver to get them out (e.g.=20
> > removing the cerntal pin or cutting a slot across them), said engineer=20
> > was supposed to replace the entire PSU (and charge the customer for it!=
> ).
> >=20
> 
> This is still the case for a lot of "no user serviceable parts inside"=20
> bits from IBM.  Billable call, and then some... 350 quid plus vat and=20
> parts, or thereabouts.

The comment on the PSU applied even if the service call was totally 
unrelated to PSU problems, If an engineer came to, say, install some RAM 
chips, he was supposed to check the PSU screws (and some other things) 
and replace the PSU if necessary.

This was, apparently, for safety reasons. IF the PSU had been opened, 
there was no way to know if any nasty bodges had been done internally...

(FWIW, I've opened IBM PSUs, I've repaired them, IMHO, properly and 
safely, and I've put the tamperproof Torx screws back in again...)


> >>Having said all that, I tend to take the same view as you when it comes
> >>to my classic car, and try and use the right bolts / screws etc.
> >=20
> >=20
> > What have you got?
> >=20
> 
> Ah, see, I don't.  I want the damn thing to work, and reliably.  If I=20
> can make it easy to fix when it goes wrong, even better.  That's why I=20
> always replace the steel hydraulic pipes with kunifer, and use stainless=20

Well, my Father's Citroen BX (touch wood...) has hard very few hydraulic 
problems. I've had to replace just one high pressure pipe (to the back 
brakes), which was damaged by an idiot garage mechanic when he refitted 
the rear subframe after an accident repair. 

> > and not that many people have a reasonably complete set of Whitworth=20
> > spanners and sockets any more.
> 
> Uhm, I do.  And it's mostly old Citro=EBns I work on, all metric (but lot=

So do I, but then I have a Myford lathe, which is assembled with an 
interesting mix of BSW, BA, and metric bolts...

> s=20
> of 7mm and 11mm bolts).

11mm is relatively common. It's 12mm that I find somewhat obscure, and 
which Citroen seem to use to excess...

-tony