HELP Needed: Restoration of an HP 5065A Rubidium Standard  - Page 1
Forum section: electronics / general

author: spaceham
author_rank: Contributor
timestamp: October 24, 2024, 07:47:14 pm
content: Good evening,I was recently given a HP 5065A Rubidium Standard by a Ham radio operator friend. Looks like an early version.He stated that it needed work and that the magic smoke had been released quite some time ago.It came without the top and bottom covers unfortunately...Here are a couple pictures of the unit attached. I have attached also a close up of the RVFR, front back etc.It seems that the smoke came from the A15 power supply module. As a matter of fact I was given two of these. An old one and a more recent revision it seems.As you can see in the included picture the bridge rectifier mod was done and is now mounted on the chassis.On one of the two A15 board has the traces cut on the Leads 12-13-14 and 15. I don't know if that is part of the mod or not.We can see the magic smoke seems to have come out of L2, that was replaced after. The 100uF caps were replaced along with the C11.On the older A15 I would need to solder L2, the 100uF caps and C11.My first question: which A15 board shall i use and work on? The recent revision or the old and modified one? What should have a look at and replace, check before i insert it?I would think getting this A15 board up and running would be a first step?Also i have seen some other tantalum caps should be replaced in various places. I have not done so yet.I have also disconnected the removed the RVFR and measured A12 RVFR 9 pin jack and measured impedance between pins 4 and 5 and pins 3 and 4. I found 50 ohms and no short to ground.Also The first slot where A2 board could be inserted is empty. Is that normal?I have read through the restoration topics but i would really appreciate some input on the first steps in need to make: what to test? and what to do on the A15 board etc etc I really want to make this one work againThank you very much for all the help

author: spaceham
author_rank: Contributor
timestamp: October 24, 2024, 07:49:50 pm
content: Some more pictures. Top and bottom and close ups of the Boards.

author: bat
author_rank: Regular Contributor
timestamp: October 25, 2024, 09:28:14 am
content: Sadly I have never touched HP rubidium standards. I have some knowledge on our current standards at work which were hand made for some odd reasons. I think you should restore the original A15 board. I don't think the modifications done to it have been documented however, HP definetely gave you alot of informations about the board in the documentation. I think you can restore it easily.The newer A15 board isn't completely new I guess, it's probably the same as the older one with updated components.

author: spaceham
author_rank: Contributor
timestamp: October 25, 2024, 09:42:10 am
content: Yes definitely, I have the complete service manual in printed version so thats helping a lot. Since the Rectifier has been added to the chassis and connected to the pins 12-13-14-15 it make sens thats the traces are cut on the Board i would guess.With L2 burn i was thinking about a short in the RVFR, but the measurements on the 9 pin connector show nothing unusual for nowThe newer A15 Board is indeed updated a bit, some newer components, I would guess i shall use that one then

author: Uky
author_rank: Regular Contributor
timestamp: October 26, 2024, 10:44:07 am
content: There is plentiful of information on how to restore an old 5065 on the internetto be downloaded. Old and newer versions of the modules inside. There isalso some helpful information on easier ways to adjust the circuitry onceyou have the basic supply functions working.

author: spaceham
author_rank: Contributor
timestamp: October 27, 2024, 11:39:39 am
content: Yes, Do you have any good links to share?

author: Uky
author_rank: Regular Contributor
timestamp: October 27, 2024, 08:27:48 pm
content: On this forum: Look for signature "5065AGuru"Then there is:http://www.timeok.it/wp-content/uploads/2015/09/First-aid-II-when-you-buy-an-hp5065A-v-1.0.pdfhttp://www.timeok.it/wp-content/uploads/2015/09/First-aid-when-you-buy-an-hp5065A-v-1.2.pdfAnd KO4BB manual download section for the 5065A

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: October 28, 2024, 04:30:51 am
content: Spaceham,Hi!First you appear to be missing either the A2 or the A18 PC card. Either one plugs into the A2 slot and provides a diode to feed power to the A15.You can add 3Amp 40V shottky rectifier on the bottom of the A2 connector, anode to pin 9and cathode to pin 8 to substitute for the pc card.The external bridge mod only requires that the 4 diodes on the A15 be removed, no need to cut traces but the cut traces won't hurt anything. As both boards have the diodes removed you are OK there.On the board with the cut traces the two transistors at the lower left of your PIX seem crunched down, make sure the leads are OK and not shorting.Once you are ready to try the A15 board place the front panel meter switch in the supply position and then plug the unit in. (the diode mentioned will need to be in place!)The supply reading should come up to a nominal 40, if way off unplug the unit and hang a DVM onto the +20V line, plug back in and see what you get.If you do have a good +20V then hook a DVM to the -20V and make sure its also OK.You should also pull the A11 module and make sure the two power resistors look unburnt.Pull the 9 pin connector from the A12 to the chassis (top of unit) and Ohm out pins 4 to 5 and pins 4 to 3 both should be around 50 Ohms. Also Ohm fro pin 4 to the threaded stud that protrudes from the front of A12. You should NOT have any continuity.Pull the SMB connector from A12 to the chassis (top of unit) and measure from the center pin of the removed cable to its shield, you should have very close to 3.33K Ohms.There is a non hermetic 100uf in A7 and A3 also and they should be inspected for visual leakage. A few more of the PC cards also have these 100uf caps. If no chemical leakage of corrosion I would just leave them be!.Once the power is OK then the photo meter reading should come up within a couple minutes after power on.The other posts I made about troubleshooting/repairing 5065A units have more good stuff.Good Luck.Corby

author: spaceham
author_rank: Contributor
timestamp: October 28, 2024, 06:07:34 am
content: That is amazingly helpful Corby! I will do all that and reply back on the thread!First off working on A15 tonight and hopefully I can move forward after"Also Ohm fro pin 4 to the threaded stud that protrudes from the front of A12." How many ohms did you mean ?Thank you again, and I can't wait to work on the unit after work tonight!

author: spaceham
author_rank: Contributor
timestamp: October 28, 2024, 11:39:11 am
content: Something else Corby, I see pins 8 and 9 are soldered together on my A2 connector, ... wierd no? You should see it on the picture i posted a bit higher in the thread. What do you think?

author: spaceham
author_rank: Contributor
timestamp: October 28, 2024, 07:29:39 pm
content: So,I have added the schottky rectifier (see the picture) and removed the solder between pin 8 and 9.I inserted the A15 card, plugged the unit and... nothing. I get absolutely no reading on the front meter in the power supply position. Any other position doesn't show anything either. the needle stays centered. I have a faint orange light for the integrator limit. And my readings are way off:Pin 1: 0vPin 2: 1.15vPin 3: 10.5vPin 4: 36vPin 5: 3.22vPin 6: 9.76vPin 7: 9.76vPin 8: 1.95vPin 9: 9.63vPin 10: 0vPin 11: -10.4vPin 12: 0vPin 13: 37vPin 14:16.85vPin 15:0vI'm a bit puzzled there

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: October 28, 2024, 11:38:01 pm
content: From pin 4 of the 9 pin connector to the threaded stud you should not have any continuity. (IE infinite Ohms)A connection between pin 8 and 9 should be OK. The diode is only needed to isolate an external supply.On the chassis mounted transistor by the A15 you should have 24 to 32 volts DC on the collector and 20 volts DC on the emitter. The A15 regulates the collector input down to the 20V level.Check the transistor and also Ohm the +20V lead to ground to see if there is a short somewhere.Cheers, Corby

author: spaceham
author_rank: Contributor
timestamp: October 29, 2024, 07:48:11 am
content: Thx for the Reply,I'm gonna have a look at this chassis mounted transistor. At the moment i disconnected and removed the RVFR from the unit. As i wanted to get this power supply up and running first.I will also post all my measurements on the connectors tonight.Cheers

author: spaceham
author_rank: Contributor
timestamp: October 30, 2024, 08:32:48 pm
content: Update:I realized I have 38v ac out of the transformer, and I realized a have 10v instead of 20v where I should have it on A15.Q1 on chassis is good , c1-c2-c7-l1-r4 are good so that brings me to Q3, and Q3 looks dead upon testing it. I removed it from the board and I have infinite reading everywhere on it. Q2 readings look weird alsoWhat reference can i use as good replacement for Q3 and Q2?Thank very much

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: November 01, 2024, 05:34:59 pm
content: Hi,The 1853-0001 crosses to a 2N1132 and the 1854-0003 crosses to a 2N1711.Both the actual HP parts and the crosses are available on eBay.I can provide you 2 new -0001 and 2 used but tested -0003 units for $10.00 + shipping if you would like.Via PaypalI'll also throw in the 1854-0020 chassis mounted transistor.Cheers,Corby

author: spaceham
author_rank: Contributor
timestamp: November 05, 2024, 09:11:56 am
content: HelloThank for the reply, I found the exact parts in my HP spares stash! for the to39 transistors, hopefully they are not trash, otherwise I will definitely buy those from you mate, lifesaver!The two zenner diodes CR9A/B are shot as well... It feels like i would save some time swapping all component for fresh ones at this point!

author: spaceham
author_rank: Contributor
timestamp: November 05, 2024, 09:08:41 pm
content: Update:I put new CR9A & CR9 diodes, New CR5 diode, New Q1, Q2, Q3,Q5 and Q4.Now the Q1 chassis mounted transistor regulates only to 13-14volts. I desoldered the leads and tested it. Wierd numbers also in the diode test mode. I suspect this last component to be the one faulty. Any action on R17 doesnt change the output voltage level. So i left it back to its original position.A15Q1 is the only transistor on the board to heat up gently to the touch but i would suspect thats normal?So i'd need to swap Chassis mounted Q1 i think. What are your thoughts?Cheers

author: spaceham
author_rank: Contributor
timestamp: November 05, 2024, 10:10:32 pm
content: And something else: the meter never moves regardless of the main switch selection. The needle juste stays centered. On power supply selection and any other selection. Maybe because I still don't have 20v but only 14v ? I would have expected it to move at least slightly

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: November 06, 2024, 12:31:18 am
content: Sound like progress.I'd check the meter movement itself as it should read maybe 28 or so with only 14 Volts.Cheers,Corby

author: spaceham
author_rank: Contributor
timestamp: November 06, 2024, 06:12:08 pm
content: Update: meter looks shot. Chassis mounted transistor looks like could be part of the issue on low voltageNew side quest: understanding why am i missing two wires to the oven xtal assy, looking at the bottom of the unit with BJ and G written with a pencil. See picture attached.

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: November 06, 2024, 06:56:28 pm
content: Those two wires are supposed to connect to 115VAC.They provide for the fast oven to decrease oscillator warmup time.Will work without but the oscillator will take longer to stabilize.Cheers,Corby