Do you have a logic probe I can beg borrow or buy?

> > 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

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. 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. 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

Indeed. Pull the boards and clean all the edge connectors (and just about any other metal-metal contact). -tony