IBM 5155 analogue display fault

[Gordon JC Pearce]

Tony Duell wrote:
>>On Fri, 2005-05-27 at 01:56 +0100, Tony Duell wrote:
>>
>>>>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...)
>>
>>It's the sort of tool that not many people have though. Why make life
> 
> 
> That is not an excuse. Anyone working on IBM 5155s (or for that matter 
> Friden Flexowriters, which are stuffed with setscrews needing Bristol 
> Spline drivers) should have a set. 

Are they the ones that are the same shape as a tractor PTO shaft?

>>difficult for the next person who comes along and has to fix the
>>machine? The only reason I can think of for using those screws is that
>>people were expected to go inside the case to swap cards every so often,
>>but they weren't supposed to be poking around in the display section.
> 
> 
> That was exactly the reason (and the reason for using tamperproof Torx in 
> the PSU). Customers were only supposed to have normal tools, Failed 
> Servoids hat the Bristol spline tools as well (but couldn't therefore 
> open the PSU case). 
> 
> According to one manual I've got, if an IBM service engineer saw that the 
> tamperproof torx screws on the PSU had been replaced with normal screws, 
> or had been moodifed to allow a normal driver to get them out (e.g. 
> removing the cerntal pin or cutting a slot across them), said engineer 
> was supposed to replace the entire PSU (and charge the customer for it!).
> 

This is still the case for a lot of "no user serviceable parts inside" 
bits from IBM.  Billable call, and then some... 350 quid plus vat and 
parts, or thereabouts.

>>That requirement's gone now; if someone owns one of these beasts these
>>days then they're presumably just as likely to be inside the display
>>section to fix stuff as they are digging around in the rest of the
>>innards; doesn't it make sense to use the same type of screw throughout?
> 
> 
> My view has alayws been to keep the machine as original as possible. This 
> doesn't mean not repairing a machine, it doesn't mean not using modern 
> components for replacements. But it does IMHO mean not replacing 
> components unnecessarily. In particular, I always replace the minimum 
> number of parts (e.g. a chip and not the complete PCB), and not replacing 
> screws with different types.
> 
> I have a set of Bristol spline keys, so I don't really worry about this. 
> I also have Torx, Allen hex, System Zero, and so on... I've found just 
> about all of them necessary for classic computer repairs.

Yup

> I would have hoped a museumwould also want to keep machines as original 
> as possible, but then again my views on Bletchley Park are well known...

Fair point there, you want it to be as original as possible

>>If the bristol-type screws were used externally or in a prominent
>>position, or exclusively throughout the machine I think I'd agree with
>>you, but the requirement to have a special tool to get to the display
>>circuitry is long gone.
> 
> 
> Well, I don't think a Bristol Spline key is any more special than, say, a 
> Torx driver...

Not if you guddle about inside old IBMS, no.

>>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.
> 
> 
> What have you got?
> 

Ah, see, I don't.  I want the damn thing to work, and reliably.  If I 
can make it easy to fix when it goes wrong, even better.  That's why I 
always replace the steel hydraulic pipes with kunifer, and use stainless 
pipe nuts (just for an example).  You can't play about with hydraulic 
fluid at 4 tons per square inch, especially if it controls your brakes too!

>>everywhere even if it's somewhere that can't be seen - but then it
>>doesn't use oddball fastenings that not many people have the right tool
>>for :-)
> 
> 
> Well, British classic cars tend to have Whitworth bolts all over them, 
> and not that many people have a reasonably complete set of Whitworth 
> spanners and sockets any more.

Uhm, I do.  And it's mostly old Citroëns I work on, all metric (but lots 
of 7mm and 11mm bolts).

Gordon.