Electronics > Metrology

HP 5065A Rubidium Standard Repair Log

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I recently got a rare HP 5065A Rubidium frequency (secondary) standard off Ebay (https://www.eevblog.com/forum/buysellwanted/fs-(uk)-hp-5065a-rb-frequency-standard-other-calibrators/). This is one of the old time goodies.

It was a "For Parts" sale and the seller didn't give much info, but it was a rare opportunity to get one of these over in Europe and shipping from the States is a killer due to their weight. So it took my chances, expecting the worst and hoping for the best. The 5065A arrived this week and a first glance revealed that (one of) the previous owners was "Devonport Management Limited". Port? Do I hear sea port? Salt water? Yes, you guessed it, mild corrosion everywhere, but lets do an inventory first.

This is a rather recent 1989 model with all options (that is option 001 and 002). Option 001 is a clock module, which gives us a, well...uhm, clock, a 1 pps output and a sync input. This is a must have for anyone who can't stand it, when the integrated clock of your favourite data logger goes out of sync. Love it! I'll never miss a second for the rest of my life.

Option 002 is a NiCd backup battery which gives you 10 minutes of battery life for a whooping 16 h of charging. We will get to that later.

Being a more recent model it also features the better 10811-60109 OCXO. Very nice indeed.

I don't have a power cord yet, but that is something Mouser can fix. Meanwhile I opened it up and took a few pictures. Unfortunately half of them are still on the mobile phone of my colleagues, so I will post them later. The first thing I was greeted with, was a bag with “loose nuts and screws” written on it – bad sign. The rubidium cell was disconnected and the wires hanging loose. The battery was corroded and had spilled its guts – yuk. But otherwise at least everything seemed to be there. Nothing missing at first glance. The first picture shows the the inner assembly, from which I have removed the battery the A6 board and the rubidium cell. You can see some of the rust I was talking about on the oscillator housing in the right bottom corner.

I checked the boards and obviously someone already had a shot a repairing them. Man, I just love it when people leave the flux on the boards...Some of the boards have new caps on them, but no cleanup was done in the areas which had signs of capacitor leakage. I will post the pictures of the boards as soon as I get my hands on them. All the boards will require new caps and some thorough cleaning to get rid of the copper oxide.

What do you guys think is best? Citric acid or vinegar? Then some sodium bicarbonate (baking soda) to neutralize, distilled water and finally IPA. That would be my strategy and everything that is left will meet my friend, the fibreglass pen.

Good Luck for repair Your 5065,
if You continue to report the progress I believe some Gentlemen will very helpful.
btw one of the very kind and talented gentlemen already looked at Your thread  ;)

no no no its not me

Mine also had the battery option and it looked about as bad as yours.  I decided not to replace the batteries, but I did keep the plastic battery holder - just in case I change my mind later.

For the power cord, don't bother with Mouser yet.  That military connector is pricey.  Just go into your junk box and find three female sockets that are close to the right size.  Solder them onto a cord, pinch them down so they're a snug fit, and heatshrink them for safety.  If you really want to, use a cable clamp to hold the cable in place so there's no strain on the connectors.  Once you've got the unit working, you can decide if you want to get the proper connector.

Regarding dead capacitors, take a look at this picture:

This isn't my unit, but mine was about this bad.  I almost didn't realize that there's supposed to be a trace under the third capacitor that passes under the two resistors and carries on to the right.  On my unit, that trace was completely gone.  Watch out for that.  I just used vinegar and then water to clean up the boards.  By the way, the picture is from this page:  http://www.niceties.com/atomic.html .


In the meantime I had a look at the lamp assembly. Oh deary me, I see mishandled PoziDriv screws. Just a reminder for everyone repairing HP gear. The usually use PoziDriv for their gear. So check your screwdrivers before digging in! The PoziDriv screws have additional radial indentations at 45° from the main cross. Do not use a Phillips screwdriver on them, ever! (Unless you are disarming a bomb and running out of time, but even then...show some respect for your gear). I can highly recommend Wera screwdrivers with the laser tip (not affiliated in any way). They have incredible amounts of grip even with damaged screw heads.

Back to topic. This is not a good sign, because Mr. NoCleanFlux was probably meddling inside. So I did a sneak peak as well. The lamp seems fine (picture 3), but what is that on the bottom side of the pcb? Can you spot it? Black marks on the mounting spacers. Uh Oh. Reminds me of IT crowd.

And of course more havok from Mr. NoCleanFlux. So yep, he was here as well. Probably trying to clean up the burn marks. See picture 4 to see what it looks like underneath. Again look closely. Hint: the black capacitor.              Crack in the middle. Next to it char marks in black on another component. Ok, I will have to rip that apart as soon as I identified the damaged parts. The red "blob" in the background is another capacitor. Broken as well...So we had quite a hot party going on here. But the good news is, that the lamp looks fine. Phew. Lets see what the vapour cell looks like. I am in luck. No broken glass. Looking good.

Yep my boards look mostly like that, with A6 in a little worse shape, which is why I removed it for now. I will check all caps and probably replace them just for good measure.

I haven't decided on the NiCd batteries yet. But I guess I am ever going to retrofit batteries, it will be a lithium ion pack. The charger board A6 is slightly charred anyway. From the schematics it looks like a drop in replacement board with a lithium ion charger should be doable.


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