SBC6120 (a build-it-yourself PDP-8 clone) grammer checked
dgy at DakotaCom.Net
Wed Jun 14 21:52:40 CDT 2006
Tony Duell wrote:
>> On Saturday 10 June 2006 05:40 pm, Tony Duell wrote:
>>> For electronic test instruments (not including hand tools, etc), my order
>>> would be something like
>>> 1) A good VOM (analogue) or DMM, whichever type you prefer.
>> You need both! Though I do tend to reach for the digital stuff more often
> I would agree, but you can get away with only one when you're starting out.
> For many years I used an analogue VOM only. To be honest, it's rare that
> you need to make an accurate meashuremnt when repairing a classic
> computer (you want to know if the 5V line is pressent and correct, but if
> it's acutally 4.95V, things will still worl fine). Then I picked up a
> cheap Fluke 85. I use that almost exclusively now, but the analogue meter
> stays on my bench, it's better for osme things.
(grin) Agreed. I've got a Fluke 8840A and it is really hard
to NOT wait for every digit on the display to settle down!
OTOH, if I pull out my Simpson 260P, the needle ballistics
are damped enough that you get a pretty quick "feel" for what
the number is.
>> than not, but that's more a matter of physical convenience than anything
>> else (little teeny DMM sits on my desk AAMOF).
>>> 2) A logic probe
>> I've not found those as useful as I'd have thought at one time. Got one here
> Tastes differ, I use one all the time. Actually, I've not used a normal
> logic probe for the last 8 years or so, that's only because I bought a
> LogicDart. But I debugged an awful lot of old computer stuff with a cheap
> Radio Shack probe, and could do it again.
I have an HP set (probe and pulser) and find them quite handy!
The biggest problem is making sure NOT to accidentally let it
touch some odd supply. :-(
Of course, it really works best with traditional TTL instead
of newer logic families (but, it's good enough to give you
a quick indication of "dead" lines, etc.
>>> 5) A 'scope or logic analyser, depending on what sort of work you're doing
>>> 6) The other one of those instruments
>> Scopes I've been using for ages, but never had occasion to use a logic
>> analyzer. Or could afford one.
> There are plenty of second-hand analyesers about that are fine for
> classic computer repairs. I have an old Gould 100MHz unit.
> As regards using it, it depends one what you work on, but I've found it
> very useful for tracing microcode in some older machines. See what the
> processor is really doing (and then work out if it should be doing it).
Problem with most logic analyzers is getting all the microhooks
(or easyhooks) that go with it. Without having to sell a kidney!
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