[time-nuts] Re: HP 5065A repair

[Matt Huszagh]

Update: I realized my unit had the shunt inductor across the TED wires
so I cut this out and am now back at the de-flooding process.

When I first started the de-flooding process yesterday, I noticed quite
a bit of 2nd harmonic meter deflection/activity, but now it's pretty
steady at 0. I'm not sure if this is normal. But, I'm not very far into
the 6-day process, so I suppose I just need to wait.

Matt

Matt Huszagh <huszaghmatt at gmail.com> writes:

> 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