Piggybacking 74LS logic chips to confirm a suspected fault

[Alexandre Souza]

It works if the gate is open. But if it is shorted to gnd/vcc, you're in
trouble :)

Enviado do meu Tele-Movel
Em 22/12/2015 19:09, "Rik Bos" <hp-fix at xs4all.nl> escreveu:

>
>
> > -----Oorspronkelijk bericht-----
> > Van: cctalk [mailto:cctalk-bounces at classiccmp.org] Namens Terry Stewart
> > Verzonden: dinsdag 22 december 2015 21:50
> > Aan: General Discussion: On-Topic and Off-Topic Posts
> > Onderwerp: Piggybacking 74LS logic chips to confirm a suspected fault
> >
> > Hi,
> >
> > I've written up my recent third Apple II repair, this time an Apple IIe.
> >
> http://www.classic-computers.org.nz/blog/2015-12-22-appleiIIe-no-video.htm
> >
> > One interesting aspect of this repair is that piggy-backing a logic chip
> helped
> > confirm a faulty one. I'd only ever used this technique with RAM.
> > I'm sure it only works if the chip has a particular type of fault, but
> it worked this
> > time for me.
> >
> > Terry (Tez)
>
> I use a HP 10529A logic comparator on regular basis for fault finding in
> ttl circuits.
> It compares a reference chip with the CUT (Chip under test;) it's a very
> nice diagnostic tool.
> It's a bit like piggy backing just a little more sophisticated :0
>
> -Rik
>
>