logic probe

From: Andrew Davie <adavie_at_mad.scientist.com>
Date: Wed Feb 25 04:57:45 1998

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 :)


-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
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
>> 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
>> 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
>> all the boards. Good idea?
>Indeed. Pull the boards and clean all the edge connectors (and just about
>any other metal-metal contact).
Received on Wed Feb 25 1998 - 04:57:45 GMT

This archive was generated by hypermail 2.3.0 : Fri Oct 10 2014 - 23:30:54 BST