[time-nuts] HP5065A digital clock info

J. L. Trantham jltran at att.net
Wed Sep 28 03:11:09 UTC 2011


The LED clock is relatively simple.  It is power, ground, and a 1 PPS pulse.
There are also some controls if the AC power goes out and the unit goes to
battery back up.  Then you have to push the button on the front to see the

The chip is a 5313.  

There are also at least two versions of the LED clock, one with three PC
boards and one with two.  I have a number of these in 5061A's and one in a
5065A, all of which are the 'two PC board' variety.  The schematics are
available in the 5061A manual and, possibly, in the 5065A manual.

I had a 'dead' clock in one of my 5061A's that turned out to be U1 (5313) on
the A2 board and was able to find the chip from one of those 'findchipsnow'
type websites from maybe 'Area 51'??  There was a minimum order of $100 and
the chips were $25 each, I think.  Anyway, I bought 4 (or whatever), removed
the dead chip, installed a socket, inserted the 'new' chip and all was well.
I have some spares if needed for what I paid plus postage, if you need one.
I'll have to go back and verify what I paid for the chips but I think I am
close.  While seemingly outrageous in price, it was easier than spending two
weeks 'rebuilding' the clock.  When encountering a dead clock, the likely
culprit is dead electrolytic capacitors and/or a dead Q3 on the A1 Regulator
Board, a 2N2905A.  Other than the one example of a dead 5313, all the other
failures have been the capacitors and Q3.

Good luck,


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of ed breya
Sent: Tuesday, September 27, 2011 12:55 PM
To: time-nuts at febo.com
Subject: [time-nuts] HP5065A digital clock info

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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