17 Jul
2005
17 Jul
'05
11:07 p.m.
In message <m1DuGKR-000IyRC at p850ug1>
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
Suppose you have a non-working HP9810 calculator
(well, it's almost a
computer :-)). You have a choice of 2 repairers.
A) Worked ofr HP as a service engineer for many years. He's got the
official service manual (which is a boardswapper guide), and can follow
the instructions which are basically to replace all the plug-in PCBs until
it starts working again. The fact that you can't get replacement boards
any more is another matter...
B) Has never worked for HP or any other computer company. But he was
given a broken 9810 a few years back and spent a couple of months working
out how to repair it. This guy can connect a logic analyser to an
undocumented internal connector and trace the CPU microcode. He's got his
own microcode listings and can thus tell just what the darn thing is
doing.
Now, who do you pick?
B. Component level debugging and repair is a rare and valuable skill. Chances
are, B could probably debug the thing down to a dead logic gate, whereas A
would probably go down to board level and go looking for a new CPU microcode
board or whatever.
There's also the point of actually knowing what your tools are telling you
and how to make the best use of the tools. It's no use knowing in how to use
an oscilloscope if you don't know how to interpret the information it's
giving you.
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
... Set phasers on tickle!