[HomeBrew] Strange anomaly of a 74LS90

Sat, 17 Apr 2004 10:22:45 -0400

Yep.
used to happen an awful lot, back in the 1980s, prototype work was done
by wire-wrap and when the thing was all done and you put chips into the
sockets, the thing wouldn't work properly. So first it was, check the
wiring then the circuit, and last the devices. Got so bad we took to the
expedient of buying an IC tester (very expensive) and having them
checked
at the incoming inspection station. As I recall we had a 5% failure rate
among various vendors. The solution was was to check everything and bag
the defective parts and send them back to the vendor for a refund. Of
course we were using lots of components, so there was no problem.

When in doubt, simply remember "Murphy", anything that can go wrong,
will
go wrong.

Jim
WB2FCN
http://eshop1.chem.buffalo.edu 

[email protected] wrote:
> 
> ** Please do NOT cross-post messages to multiple mailing lists on the "To:" or "CC:" line of the e-mail message. **
> 
> Phil,
> 
>   I saw something similar with some bi-directional versions
> of the 'LS90.  In our case, it was the 74LS192.
>   We blamed it on the 'no-name' label.  Don't remember who
> the MFR was, but it sure wasn't TI, Motorola, etc...
> 
>   I pity the poor 'newbie' that runs into things like this,
> while trying to get their 'first project' up and running!
>   It could really discourage a fellow.
> 
> 73,
> 
> Kevin
> 
>   <><><><><><><><><><><><><><>
>   Amateur Radio Station - KD1J
>   Kevin D. Jacobson
>   27 Ridge Road
>   Wallingford,    CT.    06492
>   e-Mail:       [email protected]
>   Website: http://www.kd1j.com
>   <><><><><><><><><><><><><><>
> 
> =================================================================
> 
> On Fri, 16 Apr 2004 23:14:17 -0700, "Philip Atchley" wrote:
> 
> >
> > ** Please do NOT cross-post messages to multiple mailing lists on the "To:"
> > or "CC:" line of the e-mail message. **
> >
> > Hi,
> > Today I finished building a Xtal Calibrator to use with my Hallicrafters
> > SX-71 receiver.  Kind of a "super calibrator" with both 5 MHz and 4 MHz
> Xtal
> > oscillators and dividers to give me markers at 5, 2 & 1 MHz intervals as
> > well as 500, 100, 50 & 25KHz.  (Only one of the two Xtal Oscillators are
> > active at a time). I derived the 500 kHz by dividing the 5MHz in a 74LS90,
> I
> > could just have easily divided the 1MHz by two in a 74LS74.
> >
> > Anyway, after I built it and proceeded to check it out, everything tested
> > out OK, EXCEPT for the 500KHz output (5MHz divided by 10 in a 74LS90 decade
> > divider).  That one gave me an output of about 625 kHz.  Quick math showed
> > that it was dividing by 8 instead of 10.  Double checked all the wiring and
> > connections, it was good.  I plugged in another 74LS90 (glad I used
> sockets)
> > and it worked PROPERLY!
> >
> > Has anyone here seen a decade divider (consists of a divide/5 and a
> divide/2
> > divider) that divided by 8?
> >
> > 73 from the "Beaconeers Lair".
> > Phil, KO6BB
> >
> > DX begins at the noise floor!
> > Merced, Central California
> > 37.18N  120.29W  CM97sh
> >
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