[time-nuts] HP-59309A Clock counts only seconds

[Jeremy Nichols]

I have a new-to-me HP-59309A HP-IB Digital Clock. The clock works on 
both the internal crystal oscillator and on an external 10 MHz standard 
(GPSDO). However, it counts only to 60 seconds and then repeats without 
updating the minutes digit. The TIME SET (FAST and SLOW) push-buttons 
work but again, the count will not update minutes and hours, only 
seconds. The DAY SET procedure works correctly for days and months. All 
the other switches and buttons do what they are supposed to do. Using my 
10526T logic pulser I can force the minutes and hours counters to work. 
The power supply is in good condition (after replacement of a few 
components) and I see no other problems (yet).

Tracing the clock signal through the logic circuitry brought me to U3 on 
the A4 board. This (U3) is a 4011 quad 2-input NAND gate in a 14-pin DIP 
package. It "connects" the seconds counter to the minutes counter and 
appears to have failed. One of the people on the email list 
<hp_agilent_equipment at yahoogroups.com> commented that the 4000 series 
CMOS chips have a known limited lifetime. Since these parts are no 
longer in production, the writer expressed the concern that any parts I 
might find to buy may be DOA.

Before I go hunting for parts, I'd appreciate hearing from anyone in the 
group who has experience with the 59309A Clock and/or the 4000-series 
CMOS family. In particular, are there modern equivalents to my 4011 
chip? If the 4000's really do have a limited lifetime I'd rather use a 
substitute.

Jeremy, N6WFO