[time-nuts] HP 5065A repair

[Matt Huszagh]

Hi,

I have an HP 5065A received in unknown condition. After performing some
pre-emptive maintenance (basically Corby's recommendations here:
https://www.eevblog.com/forum/metrology/inspecting-aligning-and-testing-an-hp-5065a-rubidium/
and the first aid advice from Luciano here:
http://www.timeok.it/hp5065a-corner-3/) I turned the unit on. +/- 20V
supplies look good and cell and lamp ovens drop down from pegged in
under 45 min to about 32 each.

However, the 2nd harmonic reading is 0 and of course the unit does not
lock.

This unit was left unpowered for some time (I got the sense it was at
least several years) before I received it, and therefore cell flooding
is likely. However, I have noticed a few other discrepencies.

The first is that the A3 TP2 AGC DC voltage measures 71 mV, instead of
the expected >4.5 V. I also checked the 60 MHz signal into 50 ohms and
see about 30 mW. One place in the manual says this should be >1V (which
it is), but another place says 300 mW. Is loading this with 50 ohms
correct? If so, maybe 300 mW is a typo and it should read 30 mW? In any
event the AGC DC voltage is wrong and I suppose needs to be addressed.

The second issue, and probably a more serious one, is that the PHOTO I
meter reading is 20 (less than the specified 25) and the actual current
measured out of A12 is -10 uA (should be 50 uA or greater). There are
two issues here: (1) the actual current disagrees with the meter
indication and (2) the current is low. Is the low current possibly
explained by cell flooding and or incorrect/insufficient 60 MHz RF
signal application?

Thoughts on next steps? I believe I need to address both issues
above. Addressing cell flooding is straightforward, but will take some
time. The troubleshooting section for A3 says to perform the loop
adjustment procedure if the AGC DC voltage is wrong. Which should I do
first? Or, should I start with something else?

Thanks!
Matt