Repair or Replace? [Was: Repairing Timex]

From: Adrian Graham <agraham_at_ccat.co.uk>
Date: Wed Jul 19 05:41:49 2000

> Basically they will tell you if a given point is 'high'
> (above a certain
> threshold voltage), 'low' (below a different threshold voltage),
> illegal/floating (between the 2 thresholds). They also indicate if a
> point is changing state ('clocking'), or if there's a narrow
> pulse on a particular point.

Right, so I need to know which pins of various chips do what then. Dammit -
that's more info than I have time to find ATM. Pity there isn't a 'Logic
Probing for Dummies' book :o) Once the museum room's finished and I get a
proper work area I can maybe kick back and start getting down to that sort
of level.

> The cheaper ones have fixed thresholds for TTL chips (which
> is all you
> really need) and maybe 4000-series CMOS. More advanced (and
> expensive!)

Maplins appear to do 2, one just over a tenner (ukp10) and the other at
ukp17.

> Now, as to how it's used. You can use it to find a stuck (or
> not driven
> at all) line on a data or address bus. To check if buffer
> chips are being
> enabled. To see if the output of a gate is stuck high or low,
> and what
> the inputs are doing. To see if a CPU is getting a clock signal, etc.

Definitely too much info I need to learn for now I think....

> If you want to preserve both the board and the chip, then
> first suck off
> the solder with a temperature-controlled iron (you should
> really be using
> one of these for all work...) and a solder sucker. If a hole

My gas one is temperature controlled, plus our erstwhile engineer down in
head office is retiring, so I might be able to buy some of their test kit
off them since he was the last one who could do those sorts of repairs. An
entire electronic workshop will be vacant!
Received on Wed Jul 19 2000 - 05:41:49 BST