RE: HP 10529A Logic comparator

The output of one IC usually feeds into another (or several others).

If the IC it is feeding has a shagged input, it might for example pull the
output to ground and will likely make both of them look shagged.

Think about how the logic comparator works - all it's doing is driving a second
IC with the same inputs as the IC under test, and comparing the results, and any
glitches of a certain size get 'stretched' a bit so you can see them.

However, (I think) that the output of the comparison IC isn't connected to the
rest of the PCB so there could be other stuff there that could cause problems,
e.g. lots of capacitance.

I'm not a 10529 guru, but I've had occasions where the tests fail, and I've
always managed to dream up a reason why.

Remember also that some 74 ICs have flip-flops in them, so they can get into the
wrong state if you don't start from power up.

Phil

> -----Original Message-----
> From: owner-techtoolslist@flippers.com
> [mailto:owner-techtoolslist@flippers.com]On Behalf Of Martin White
> Sent: 29 March 2004 20:19
> To: TechToolsList@flippers.com
> Subject: HP 10529A Logic comparator
>
>
> Has anyone ever made a specific list of 74 series chips that this cannot
> successfully diagnose?
>
> Or does it depend on the circuit in which they're placed (what the inputs /
> outputs are tied to)?
>
> I seem to remember being told once that it can't always successfully diagnose
> certain logic chips. I don't have enough field experience to know when i use
> it if the results I'm getting indicate a faulty IC or just an IC it can't
> reliably diagnose. In fact, so far i don't think it's been of any use to me
> whatsoever.
>
> Obviously i'm ignoring those with more than 16 pins!
>
> More specifically, i was looking at some 74LS157's the other day that
> are part
> of a 2 to 1 multiplexer prior to some ram ICs. The one that had the WE lines
> as two of the outputs was showing a fault on both of them, but replacing it
> made no difference, i thus assumed the comparator was giving a false positive
> (or negative!).
>
> Was this right, or should i really continue to suspect that IC? It's
> definately in the part of the schematics where my problem lies.
>
> Please excuse if it's a bit of a dumb question to some, but i'm merely trying
> to familiarise myself better with some of the tools that i've picked up over
> the course of the last few years.
>
> Thanks,
> Martin.
>
> If you ever want to (un)subscribe yourself with TTL, you can send mail to:
> <Majordomo@flippers.com>
> with the following command in the body of your email message:
> (un)subscribe techtoolslist
> or from another email account, besides xxx@yyy.com:
> (un)subscribe techtoolslist xxx@yyy.com
>
>

If you ever want to (un)subscribe yourself with TTL, you can send mail to:
<Majordomo@flippers.com>
with the following command in the body of your email message:
(un)subscribe techtoolslist
or from another email account, besides xxx@yyy.com:
(un)subscribe techtoolslist xxx@yyy.com
Received on Mon Mar 29 16:54:03 2004