7 Jan
2006
7 Jan
'06
5:20 a.m.
In message <m1Ev2mD-000IyIC at p850ug1>
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
I hate t osay this again, but the most important tool
for debugging is a
brain :-). I feel that a good engineer/hacker armed with an LED+resistor
logic probe is likely to do rather better than an idoit or novice (these
are NOT THE DAME THING!) armed with the most expensive 'socpe and
analyser available.
Yeah, LED+resistor debugging is fun. Downclock the CPU to a few Hz and watch
the data bits fly by :)
1) A multimeter. Digital or analogue, the choice is
yours (I have, and
use, both). It is rare to need to make accurate measurements in classic
computer work, so analogue is OK, and in fact better when you want to
'peak' the voltage at some test point or something like that. If you go
digital, I would certainly consider a Fluke.
Avoid the cheap little "pocket" meters though. If it isn't a Fluke,
it's
likely to be horrendously inaccurate at best. I once had a cheapie DMM that
was about 1.5V out on the 3V scale, and 5V out on the 30V scale.
Fluke 25 and 27 ruggedised DMMs are starting to appear on the surplus market;
seems most of them are ex-military stock. They're pretty rugged, but also
rather heavy. I've got a Fluke 25 that's been dropped a fair few times, and
still works perfectly.
I've also got a Solartron 7150plus. Very nice bench DMM, but watch out for
the power line filter module. The capacitors inside are getting old and tend
to go bang, leaving a thick coating of soot on virtually all the power supply
circuit when they blow. Schaffner still sell them (via RS), but they're ?45 a
throw IIRC. You could replace the capacitors, but good luck getting the case
open.
If you are a
rich enthusiast, consider attempting to find an HP 'Advanced Logic Probe'
aka LogicDart. It's a handheld thing that acts as a digital voltmeter,
frequency meter, logic probe and 3-channel logic analyser. A word of
warning, if you ever use one of these you will be 'hooked'....
*drool*
Or if you don't want to buy one, design your own. I've got (somewhere) the
schematics for a 20MHz 8-channel logic analyser/logic probe based on a
Gameboy. I still need to write the software, but the logic side of things
looks OK.
3) A 'scope. I would always consider Tektronix
here. Actually, I rarely
use a 'scope, other than for disk drive alignments and PSU repairs,
neither of which need a particularly highly spec'ed instrument. Mine is a
very old, valved, Tektronix 555 with an assortment of plug-ins. If I was
buying now, I'd consider getting a second-hand 7000 series or 460 series.
Nothing much more recent, IMHO Tektronix went way downhill when they
stopped putting schematics in the user manual.
The 466 is a nice little scope. 100MHz, dual channel, dual timebase and
analogue storage. Not as nice as a DSO, but a hell of a lot cheaper, and just
as usable. The trace is a little fuzzy though, thanks in part to the storage
CRT. Still perfectly usable, though, and the storage function makes it easier
to get photos off the screen.
4) A logic analyser. Tektronix made a reasonable one
as a plug-in for the
7000-series 'scopes. HP and Gould also made analysers, either stand-alone
or as plug-ins for 'scopes.
HP 1651Bs are very nice - 32 channels, but make sure it comes with the pods
and grabbers! Agilent still sell pod/grabber kits, but they charge insane
amounts for them - upwards of $400. On e-OverPay, they're hard to find at the
best of times. I've got two pods, two of the woven pod-to-analyser cables, a
pack of grabbers (only enough for one pod though) and a bag of replacement
probe cables.
System disks can be rebuilt with a DOS PC and a copy of ImageDisk (it's
actualy faster than LIFUTIL). As long as the machine passes the powerup
self-test, it's probably fine.
The ability to transfer the captured data to another
computer for more
analysis (often via an RS232 or GPIB port) is very useful
The 1651B can do this, but I haven't made an attempt to decode the
acquisition data that it passes over GPIB.
Inverse Assemblers are also fun to play with - I've got one that I threw
together for the 6502, and IIRC Jim Kearney has done one for the 8008.
I have several analysers, but the main one is a Gould
K100D (I think the
manual is on Bitsavers). 16 channel, 100MHz. I have never needed anything
more
I had a Gould analogue oscilloscope at one point - an OS1100A. Very nice
machine, 30MHz dual-trace with delay-sweep. Lovely little machine. A little
sensitive to cold though - if the temperature goes below 10 C, it won't even
power up.
5) An EPROM Emulator. I put this under test equipment
because it's very
useful to replace the ROMs in a system with an emulator containing a
little test program (even something as simple as a jump to itself), and
see what happens. I built my own, they are not complicated.
Same here - there's nothing like the sense of achievement you get when
building your own test equipment. Plus the fact that having designed and
built it, you also have all the information you need to repair it.
I've put full schematics for my EPROM emulator online - I actually entered it
into the PICLIST.com design contest last year.
<http://www.piclist.com/images/boards/EPROMemuMk2index.htm>
The Mk1, BTW, was a very fussy parallel-port thing that emulated a printer.
It had the annoying quirk of running fine on my laptop, but refusing to work
with anything else. Hence the swap to RS-232 on the Mk2. Yes, there's a
PICmicro running it, but the source code is available and pretty well
commented.
--
Phil. | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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... I will not steal this tagline, it eez scratched.