Piggybacking 74LS logic chips to confirm a suspected fault
jonas at otter.se
Fri Dec 25 11:06:58 CST 2015
>> -----Oorspronkelijk bericht-----
>> Van: cctalk [mailto:cctalk-bounces at classiccmp.org] Namens Terry
>> 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
>> I've written up my recent third Apple II repair, this time an Apple IIe.
>> One interesting aspect of this repair is that piggy-backing a logic
>> 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
In my experience, the type of socket you used is quite unreliable and
will tend to develop bad contacts. There is a reason they are cheap... I
would use a turned pin type socket instead, e g an Augat socket. They
will not let you down. More expensive, but considering the work involved
in replacing a socket and the risk of messing up the PCB, the cost is
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