HP 5065A Rubidium Frequency Standard - Successful Repair - Page 1
Forum section: electronics / general

author: edpalmer42
author_rank: Super Contributor
timestamp: May 09, 2020, 09:13:52 pm
content: My 5065A failed recently. With 5065AGuru providing advice and cheering me on, I was able to repair it. Since Corby said that my failure was unusual, I thought I'd document thethreeproblems I ended up fixing for the possible benefit of other owners.My 5065A is a late vintage unit with a serial number prefix of 2816A which suggests a manufacturing date of 1988 or 1989. I've had it since about June, 2017. Initially, it had the typical bad Ta capacitors plus a few other minor issues. Initial repairs went quickly and it's been working well since.Last month (Apr. 2020), the Continuous Operation lamp went out and the Integrator Limit lamp came on. According to the manual, that means the OCXO has drifted and needs adjustment or the A1 Synthesizer has failed. Neither was the case with my unit. All the Circuit Check values were good.Eventually, I discovered that the two main filter capacitors C2 and C3 (2800uf @ 40V) had rotted away. I replaced them with a couple of NOS Rubycon USR 3300uf @ 100V 85C that I had in my junk box. I also took the opportunity to replace the RIFA mini-bombs that were on the power line.After replacing the capacitors, I still couldn't get the Continous Operation lamp to turn on. It turned out that the lamp - which had been working fine - decided that this was a good time to burn out!I replaced it and the unit started locking, but I still had problems.My Second Harmonic meter reading was wildly unstable and eventually disappeared completely. I suspected the A7 AC/Signal Amplifier, but couldn't find any problems with it. I had earlier measured the DC current coming from the photocell as a healthy -70 ua compared to a spec of "approximately -50 ua", but now that was gone, too. That meant that either the lamp or photocell had failed. I opened the oven and found the problem in the lamp oscillator. R3 is soldered to two forked terminals that are typically used for selected components. This isn't documented so there's no info on what it was selected for. The terminals are riveted into the circuit board. On mine, one of the rivets was making intermittent contact with the board - they weren't soldered, only riveted. I soldered the terminals to the board, reassembled everything, and it finally worked.Lastly, I realigned the unit according to the manual. No drama there.I didn't take any pictures. When I'm deeply focussed on troubleshooting a piece of equipment, the last thing I want to do is break my concentration by stopping to take pictures.

author: TiN
author_rank: Super Contributor
timestamp: May 09, 2020, 09:17:09 pm
content: QuoteQuiet sigh

author: notfaded1
author_rank: Frequent Contributor
timestamp: May 10, 2020, 08:52:28 pm
content: Glad you got it fixed Ed. I surely know how important and hard to find one of those is so keeping it working is of major importance!Bill

author: bsdphk
author_rank: Regular Contributor
timestamp: May 11, 2020, 12:14:59 pm
content: Speaking of burnt out lamps, does anybody know where to get replacements these days ?

author: edpalmer42
author_rank: Super Contributor
timestamp: May 11, 2020, 05:24:46 pm
content: Quote from: bsdphk on May 11, 2020, 12:14:59 pmThese lamps don't burn out. As long as they're not physically damaged, they last for decades. Sometimes they darken a bit but, if that causes a problem, there's info online about rejuvenating them with a heat gun. I haven't had to try that.If you really have to replace a lamp, the only place to get a replacement is from another standard. In general, each model is unique.

author: notfaded1
author_rank: Frequent Contributor
timestamp: September 08, 2020, 04:11:03 pm
content: Ed,Do you keep your 5065A on all the time?Thanks,Bill

author: edpalmer42
author_rank: Super Contributor
timestamp: September 08, 2020, 11:05:31 pm
content: Yes, it's on 24/7.Quartz and, to a lesser extent, Rubidium Standards benefit from being on continuously. The components reach thermal equalibrium and have a chance to 'bake out' anything that wants to come out. This improves stability and may reduce noise levels. A Rb standard doesn't have any defined wear-out mechanisms like a Cesium does, so being powered continuously doesn't wear it out. It's worth noting that many Quartz and Rb standards don't have power switches. This tells me that the manufacturers expect them to be powered continuously.

author: notfaded1
author_rank: Frequent Contributor
timestamp: September 09, 2020, 03:09:07 pm
content: Thanks Ed! I recently got a 5065A that has the 10MHz upgrade and am learning the ropes of these.I'm hoping this can be my master reference I leave on so I can put the 5071A and 5061B to sleep to conserve the tubes and only turn on once in a while... although the 5061B I can turn off the Cs and it still keeps pumping the tube down. I haven't figured out, yet, how to do this with the 5071A but I assume there must be a way to keep it pumping down the tube while still saving the Cs. I don't mind the electricity if they can stay pumping down the Cs tube.One thing is for sure the 5071A has a LOT more data you can get out of it. Tom VB was telling me some settings to make it log regularly so I can track it's progress. I found it doesn't do this by default... at least mine didn't.Regards,Bill