[time-nuts] HP5065A digital clock info

ed breya eb at telight.com
Tue Sep 27 17:54:43 UTC 2011

I am restarting an old project to transplant my HP Z3801A guts into a 
5065A carcass, and now designing the power system. I'd like to keep 
the original LED clock function, but with all new power and 
interface. I traced out the circuit partially a few years ago, and am 
going by the notes I made back then.

The clock IC is a 28 pin DIP, marked with the National Semiconductor 
logo, and only the code "025B." I assume it is a standard clock IC of 
the era, probably PMOS. Does anyone know the true part number? I have 
never seen a 5065A schematic or parts list. The HP part number may 
help if it can be cross-referenced. I have looked at data on a number 
of National and other clock ICs from back then, and saw none that 
seem to match what's in there.


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