Comment on 'boardswapping' as part of the computer culture.

[Scott Stevens]

On Fri, 28 Oct 2005 02:29:03 +0100 (BST)
ard at p850ug1.demon.co.uk (Tony Duell) wrote:

> > 
> > I'll wade in with my comments now.......
> > 
> > Board swapping is a useful method for high reliability systems (I work in
> 
> I hate to say this, but _random_ boardswapping, which is what I am really 
> complaining about -- that is, when you easter-egg parts until the machine 
> seems to work again -- is the last thing I hope would be used on critical 
> systems. 
> 
> Unless you know what/where the fault is, you can't know you've fixed it 
> IMHO (I've explained the problems many times before).

With a proper 'boardswapping guide' and strong documentation and training, the tech can be assured that the fault is isolated to the board in question.  Then, as a _team_member_ he passes the faulty board along to someone whose specialty is to isolate it further, down to the component.

> 
> [...]
> 
> > Now back to our systems! With the above in mind:
> > 
> > 1. we rarely know the state of any parts we have - a board that has been
> > un-used for 20 years is quite likely to be faulty!
> 
> Even worse when you're trying to make one good machine out of 2 defective 
> ones and you haven't a clue as to which boards are good or not.
> 
> Note that I have no problem at all with 'test rigs', which often are 
> working examples of the machine in question that you can plug defective 
> boards into for testing. A good example of this is for the HP41 
> calculator. Due to the mechanical construction of that machine (the 
> inter-board connectors are clamped by the case screws), it's impossible 
> to have the machine in a working state where you can probe pins of the 
> chips. HP serice centres had a 'test calculator' which, from the picture 
> in the serviec manual was a mechanically modified HP41. An afternoon in 
> the workshope with a battered 41 produced a workable substitute.
> 
> > 
> > 2. We are self trained on these systems. If we can narrow a fault down to=
> >  a
> > board, we can often take it down to the component.
> 
> Actually, this is a great advantage. A lot of 'training' is based on 
> known or common faults, and if you're not careful the serviceman will get 
> totally lost when faced with something that's not been considered. Since 
> we don't get the manugacturer's traing, we (or at least I) approach such 
> problems from the viewpoint of standard electronic principles and are 
> less likely to get totally confused (well.... that's another story :-))

But the machines you enjoy working on wouldn't have ever come into existence if the company that built them had relied on small teams of artisan technicians who know EVERYTHING about them to service and maintain them.  There are layers to the big organizations that come out with sophisticated technologies.

There need to be 'grunt' foot soldiers who know how to pull a board from the chassis, replace it with a known good board, and ship the board back to the repair depot where an expert will pinpoint the problem down to a specific chip and send feedback to engineering so the new Rev. J board will have the new U-11 with the corrected PAL equation in it.  We aren't a race of supermen where every tech can know everything.

> 
> > 
> > 3. We are lucky to have any spares!
> > 
> > Looking at a less than vintage system, for the most part, it is difficult=
> >  if
> > not impossible to go below board level ( I can sympathise with Tony here)=
> > ,
> > and nigh on impossible to get information on how that board is working, o=
> > r
> > even get test equipment that can capture the signals involved (I have a
> 
> Hence my comment that I don't have a modern PC because I can't afford the 
> test gear I'd need to maintain it.

A man is not an island.  The fact that you _personally_ cannot tear down and completely rebuild a particular machine should not prevent you from understanding that somebody can, and become a part of the community that somebody exists in.

I wear what I consider to be a fairly nice Gruen wristwatch.  I don't have the skill and capability of dismantling and servicing it.  Not being able to service it doesn't lead me to refuse to wear it.  Yes, there are high quality vintage pocket watches I could use instead that I *would* be entirely capable of servicing.

> 
> > 100MHz (valve) scope with a 4 trace plug-in, or I can borrow a very old
> > logic analyser from work). At this point, we are reduced to board swappin=
> > g
> > as the only option, though often with little measurement to back it up - =
> > the
> > only thing we have over the teenager in PC World, is that at least we hav=
> > e a
> > multimeter and can check the power supply voltages........
> 
> Hmmm... I'll go a bit further than that. There is a suprising amount you 
> can do on a modern machine with limited test gear intellegently used...
> 
> > 
> > We are also at the point where PC components are so cheap they are not wo=
> > rth
> > repairing - I can buy a LAN card for less than =A310. It costs me more th=
> > an
> > that to pay an engineer to replace it, let alone try and repair it. Even =
> > the
> > kid in PC world expects =A35 an hour - if you try and charge some one =A3=
> > 50 for
> > changing a LAN card, you'll soon be out of business
> 
> Hmmm.. I have a fairly well-stocked junk box, but it contains components, 
> not boards. Suppose a serial port fails. OK, it's going to take me a 
> little longer to find the defective 1488 (or whatever) rather than just 
> swap the board _but_ it takes less time than me going over to PC-world or 
> whererver to get that replacement board. 
> 
> Of course the fact the PC-world doesn't sell boards for any of the 
> machine I own is a secondary issue :-)
> 
> -tony


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