[time-nuts] Re: HP 5065A repair

[Matt Huszagh]

I've decide to start by addressing the cell flooding. Despite the
incorrect AGC DC voltage, the 60 MHz signal looks roughly ok and from a
quick look I don't think I can really perform the loop alignment without
some sort of RVFR signal.

I've attached a current-limited supply at 5V through a 5ohm power
resistor to the TED wires and have the unit powered with the meter set
to 2nd harmonic. The meter indication almost immediately started
deflecting off 0. It's been just a few minutes and the readings are
getting almost to 10 at max deflection, though deflecting back and
forth. I'm hopeful this is a good sign. I'll update as this unit has
more time to de-flood.

Please feel free to make suggestions if I should be following a
different approach at the moment.

Thanks!
Matt

Matt Huszagh <huszaghmatt at gmail.com> writes:

> 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