[HomeBrew] Strange anomaly of a 74LS90

[Philip Atchley]

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