Re: HP 10529A Logic comparator

Yup comparing like for like.

One of the guys forwarded a link to me about the bug trap comparator, and that
suggests the 157 should compare okay. At the end of the day i'm not overly
fussed about the fact the comparator showed two of the outputs as being bad.

They both drive the WE lines of two ram ICs each, so i assume they must be
good or the graphics would be totally up the creek? Ie, if the WE wasn't
letting the ram be written to at the correct times then i guess i'd be seeing
a fair bit more of a problem than just the wrong objects being displayed on
some levels.

Was only really asking as this pcb is starting to drive me nutty!

My Fluke doesn't seem to want to know with the boardset, so that's out (ie, i
can't get it to run UUT). I've looked all over for stuck bits and can't see
any. Then for good measure this evening i've just checked the junction drop
of every pin of every IC on the board. Nothing.

Starting to scratch my head a little now! All interconnects are also good.

Admittedly, the one thing that i haven't done which i'd like to is shotgun the
object ram's socket's. Sadly they're the size in between eprom size and ttl
size and i don't have any. I guess i could split some normal ones in two, but
that's for tomorrow. Had enough for tonight :O)

Not sure if i already said or not as i got confused about reply destinations
earlier(!), but it's the video generator pcb of an MCRII set. Tron in fact.

Martin.

On Monday 29 Mar 2004 22:49, Phillip Eaton wrote:
> One more thing to add... you are comparing like with like?
>
> I don't know from experience, but if you compared an 74LS (Low Power
> Schottkey?) with a 74HC (High Speed ???) then you would probably get output
> comparison glitches caused by the speed differences.
>
> I don't know if this would tigger an output error flash, though.
>
> Welcome to analogue digital electronics :-)
>
> 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.
> >
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Received on Mon Mar 29 17:58:54 2004