I asked my boss if he had a logic analyzer i could beg borrow or buy... his
reply below.
Do you have a logic probe I can beg borrow or buy?
I have quite a fancy 32-channel 100mhz unit, which I haven't used for many
months. At around $8000 you would probably prefer to borrow rather than buy
it... Mine is a 110v unit, so you'd want to remember to use a transformer...
So, I'm assuming I'm set for a logic probe. !!!!!!!!!!!!!!!!!!!!!!!!!!
WOw. Can it make tea and coffee too? At THAT price it better.
Now for the Multimeter :)
Cheers
A
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Wednesday, February 25, 1998 10:13 AM
Subject: Re: a brain... my kingdom for a brain?
>
> Tony's comment, below... about the only equipment needed to repair... was
> helpful.
> So, as I have an Altair, a BBC, a KIM, a Sorcerer and various other
beasties
awaiting
ressurection, and having little (well, OK... no) electronics
experience, starting at square 1...
a) What should I be looking for in a logic probe. Any recommended models
(say, <$100)
I did a lot of repairs using a very cheap Tandy/Radio Shack/Micronta
logic probe, which was officially a 10MHz unit (although it would do a
bit more than that). It only cost about $25, I think. Note that there's a
logic pulser (the equivalent of a signal injector) in the same range
which is a lot less useful than the probe, so if you go for this one make
sure you're buying the right unit.
HP make some beautiful logic probes, but alas I've never seen one cheap
enough to be worth buying. They do turn up at radio rallies, though.
It's 8 times your price range (!), but the HP LogicDart is excellent if
you are serious about repairs and doing new designs. Probably total
overkil for repairing micros, though.
As regards specs, all you really need are TTL thresholds (you don't find
much else in micros - ECL is useful for some minis and workstations, but
few cheap logic probes have that), and pulse detection down to (say)
100ns or better. Just about any logic probe will do.
b) Ditto for multimeter.
Again, you don't need too high a spec - high accuracy is not that useful
in most digital work.
Analogue or Digital display is fine. I have both - the analogue meter is
better for looking at
What you need are :
DC voltage ranges up to about 50V (you only need higher voltages if you
repair monitors, etc). A sensitivity of 20000 Ohms/volt (== 50uA fsd
current) for an analogue meter would be fine. Any digital meter would
have a low enough input current.
Ohms - especially a good continuity tester. A lot of faults are broken
wires, defective switches, etc. Make sure the continuity tester responds
quickly - you want to be able to clip on probe onto (say) a connector
pin at one end of a cable and run the probe down the pins at the other
end. If you have to stop for a few seconds on each pin you'll soon go mad.
Again, that's a pretty low spec. AC voltage (up to mains) is useful for
checking transformers in linear supplies. Current ranges can be handy for
checking PSU load, etc. But I would estimate that 90%+ of all my
measurements are either DC voltage or resistance.
If you can afford it, get a Fluke (a 77 or a 79 would be _very_ nice).
AVO is another good brand. And although I've never used one, there's a
meter from Tektronix which is probably good.
If those are out of your price range, then just about _any_ digital meter
costing about $50.00 would be fine. It won't be as robust as the Fluke,
it won't be as accurate. But it'll be enough for most repairs.
A recomendation. Get a cheap-ish meter like I've just recomended. When
you get more experience and want something better, get the Fluke. Put the
cheap one in the car for checking bulbs/battery/fuses/etc when you break
down.
c) Where can I find a brain? :)
I wish I knew :-). Mine needs upgrading :-)
If you want a book recomendation, try 'The Art of Electronics' by Paul
Horrowitz and Winfield Hill. There's also a practical book 'The Student
Manual for the Art of Electronics' by (I think) T. Hayes and P.
Horrowitz. These books cover everything from resistors to
microprocessors, and have an intuitive rather than mathematical approach.
But you won't 'grow out' of them - there's a lot of good sound
information in there.
> Actually, the Altair will be my first task. I'm thinking of #1 taking
out
all the
boards. Good idea?
Indeed. Pull the boards and clean all the edge connectors (and just about
any other metal-metal contact).
-tony