[time-nuts] Re: HP 5065A repair

[Matt Huszagh]

There are a few other things I wanted to mention.

I checked the DC voltages around the cell and lamp heaters. J15P3 (cell
heater) measured 15.4V and J15P5 measured 14.4V. P4 measured 28.6V. The
specified nominal voltages for P3 and P5 are 18V, so these are a bit
off, but since the heater currents look ok as measured by the front
panel meter, I got the sense that this is probably ok. Thoughts?

Also, as part of the pre-emptive maintenance I replaced the lamp
assembly film resistor and, in the process, disassembled part of A12
including the lamp assembly. Everything looked fine to my eye and I have
pictures I can share if desired. In particular, the lamp assembly was
not charred.

Matt

Matt Huszagh <huszaghmatt at gmail.com> writes:

> 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