Boardswapping and debugging (was Need contact...)

[Philip Pemberton]

In message <m1DuIUj-000IyPC at p850ug1>
          ard at p850ug1.demon.co.uk (Tony Duell) wrote:

> Perhaps I should have re-phrased that question. Who do you pick if all 
> you've asked about is what experience A and B have of the machine. _On 
> paper_, A seems to be the better 'qualified' -- he worked for the 
> company, he's got the official manual.

He's also got no experience doing component level repair.

> In practice, you'd want B.

"The boardswapper goes looking for a display control board. The engineer goes
looking for a TIL311"

> Odd you should pick that one. The CPU control board -- 09810-66513 -- 
> which contains the microcode, is the only logic board I've not had to 
> repair in a 98x0 machine.... Still, I am sure they can fail.

I just picked the words "CPU microcode board" off the top of my head - I
suppose "display board" would have been a better choice.. meh.

> Oh, absolutely. Good test equipment is useful, but it's not essential, 
> and it's not a substitute for knowing what you are doing. Many people 
> (not on this list I hasten to add) seem to think there's a magic box you 
> can connect to a brokent <foo> that will tell you exactly what's wrong 
> and how to fix it. Of course there isn't.

I've had people ask me to find faults on their PCs...

"You're not going to use the oscilloscope?"
"Why bother? I can tell from the power LED that the power supply is cutting
 out. I've only got the multimeter out to confirm my initial assessment of
 the situation."
"Oh."

(yes, this actually happened - twice - once with a PC, and again with someone
else wanting me to "fix" their radio - dead batteries...)

> It is often possible to get the evidence you need without fancy test 
> equipment. The person who moans 'I could fix this if only I had a logic 
> analyser (or storage 'scope, or...)' is probably wrong. Not because such 
> instruments are not useful, they are. But becasue even if he had them, 
> he'd not be able to interpret the display. If he had the skill to do 
> that, he could probably manage without the instruments.

Then there's the fun of dealing with a fault that an LA won't detect. An LA
tells you if the line is high or low, and what its timing relationship is to
other signals. It can't tell you if the clock line is suffering from ringing
or overshoot...

Later.
-- 
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem at philpem.me.uk              | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.me.uk/          | 48xCD, ARCINv6c IDE, SCSI
... One way to better your lot is to do a lot better...