[time-nuts] Repairing an HP 5065A Rubidium Vapor Frequency Standard. Sharing experience and advice welcome.

[Jean-Charles BILLEBAULT]

Hello time-nuts,

First, thanks to this amazing community and especially the extensive archives which have been invaluable for my HP5065A work so far.

I'm knee-deep in another 5065A repair and running into some issues I'd appreciate input on, especially from anyone who's dealt with heater wire sourcing but also anyone that ever dealt with this peace of art.

So one day we smell that odor we easily recognize. After verification , there’s C1 short in the RVFR - no big deal, swapped it out with a 2499-003-X5W0-502PLF and that part's sorted. But of course, the short had enough time to cook the A12 assembly pretty good. The oscillator circuit inside got toasted but the component values are still in spec, just looks like it went through a barbecue.

Here's where I'm scratching my head - I'm seeing 85MHz from the A12 oscillator. Some pages in the manual mention 100MHz, others say 90MHz on the module description. Anyone know if this matters much? The lamp fires up fine after cleaning everything up, but should I be tweaking this oscillator? However it seems to me that it was brighter some years ago. Maybe I’m wrong.

The C1 failure also took out R2 and L2 in A15 from the current surge. Replaced those and the board seems happy enough despite looking a bit crispy. I'm guessing the protection circuit tried to do its thing but wasn't quite enough.

Now here's the real headache - after putting it all back together, HR1 decided to join the party and went short circuit. This almost killed the 1.5Ohms resistor and the driving transsitor had less luck.  Reading 1.2 ohms instead of 52.3 on the heating resistor, not good. Used thermal imaging to track it down and it's buried somewhere inaccessible in the heater assembly. Had to tear the whole heater body apart, found the damage, but it's toast. Tried to salvage the heating resistance during disassembly but that just created more shorts along HR1 , I think the insulation is cooked.

At least RT1 survived, so there's that.

So I contacted Peilican the wire manufacturer directly about 2332ADVFEP.009BL. Their response nearly gave me a heart attack - $700 for 300 meters or $500 for 30 meters. Has anyone actually had to bite this bullet? Please tell me someone's found a more reasonable source or figured out a way to buy smaller quantities. If we have no alternative we’ll go this way .

This is the 7th time I've had this particular unit on the bench - mostly caps, transistors, the usual suspects. Each time it's come back to these levels so for me it’s fine.
2nd harmonic
error
control
5MHz
photo I
OSC oven
cell oven
lamp oven
supply
30
0
-2
6
40
0
28
26
40



Once I get this thing breathing again, planning to do Corby's Super conversion on it.

A couple other things while I'm asking - are there any mechanical drawings floating around for the 780nm lens mount hardware for the Super mod? And has anyone tried different optical filters and found one that works particularly well? I mean there a reference for an Edmund lense 780nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter , but would a tigher bandwith be better ? Like this one FBH780-3 from thorlabs which is 3nm bandwidth.

I’m not an optical guy so I can’t tell much about this.

Also, since my A12 oscillator is pretty well cooked, has anyone ever reproduced the A12A1 PCB and managed to salvage just the A12A2 part (lamp and coil)?

Any thoughts or war stories appreciated. This one's turning into quite the project.

Thanks,

Jean-charles BILLEBAULT