HP 6114A Newbie Repair - Page 1
Forum section: electronics / repair

author: hifiguy99
author_rank: Contributor
timestamp: January 29, 2021, 03:49:00 am
content: Hi all,I have an old HP 6114A. I have a few things I noticed that are wrong. I am inexperienced with vintage electronics and any input I would appreciate.I have an imgur album here:https://imgur.com/a/RlH44oHIt seems I can't upload the pictures here directly as they are too big.It buzzes quite loudly from the transformer. I assume this is typical of equipment this old, correct?.The PCB is black. I mean not the entire PCB but I have no idea what would cause this exactly. The top underside panel is darkened in two spots. In does release some heat. Is this a major issue? See the picture:You can see the distinction here:As for any of the capacitors, should I replace any of them? I know tantalums go bad with age. I assume they are the yellow ones axial ones? Should I just leave it till one goes? None of the caps on the top side or mains side seem budging:Lastly, if I halfway press the 2nd digit on the decade switch or if I switch voltages around too quickly, it jumps to a random voltage different than what is selected - usually higher. The meter shows it accurately though. Sometimes when normally switching voltages it will spike instantly and go back to normal.Would a cleaning of the decade switch usually fix this? Example:Thanks!

author: bob91343
author_rank: Super Contributor
timestamp: January 29, 2021, 07:13:19 am
content: That 10W resistor is clearly too small. It's probably dissipating several Watts, like around 100 mA through it for nearly 80V drop. Its paint job has boiled off onto the cover. Look in the manual to see what the voltage across it should be and that will tell whether it is a bad design or a problem elsewhere.As for the switch problem, it does appear a cleaning is in order.The transformer buzz is due either to the overstress implied above, or that the bolts holding the laminations together have loosened.

author: wn1fju
author_rank: Frequent Contributor
timestamp: January 29, 2021, 12:38:00 pm
content: Your board doesn't look too bad to me. I've attached a picture of my closely related HP 6115A power supply. I wouldn't start replacing capacitors unless one (or more) is obviously spewing out electrolyte or voltage measurements show something is wrong.You will need to remove the digit switches, dissect, clean, and reinstall. See a pictorial in the eevBlog post:https://www.eevblog.com/forum/testgear/hp-6114a-precision-power-supply-restoration/

author: garrettm
author_rank: Frequent Contributor
timestamp: January 31, 2021, 02:22:21 am
content: I would use an oscilloscope to check that the programming switches aren't causing large spikes / drops in the output voltage. One unit I had would jump around wildly until I cleaned the switches. Turns out the lubricant had dried up and was causing problems with the rotary contacts mating with the PCB pads when setting the voltage.Also, you should clean the slide switch contacts, my analog display was acting goofy until those were properly cleaned too.I've owned three of these power supplies, one of which was silent, the other two had noticeable transformer hum but one was much louder than the other. So the loud hum might just be an unlucky unit rather than indicating something is wrong.I've made a imgur gallery with photos from my repair. Hopefully they can help you with yours.https://imgur.com/a/sf8hrbu

author: hifiguy99
author_rank: Contributor
timestamp: February 02, 2021, 02:14:29 am
content: Quote from: bob91343 on January 29, 2021, 07:13:19 amYour are correct in that the resistor is small. I am lazy though and just cleaned off the paint off the surrounding components with some isopropyl alcohol and a Q-tip. The Q-tip could not remove the black paint caked on the motherboard though. I didn't try other solvents. Thanks anyways.Tightening the bolts that hold the transformer do not help unfortunately.Quote from: wn1fju on January 29, 2021, 12:38:00 pmI dissected the mechanical decade switch and used dexoIT gold on the contact plate and some Non-Stick Dry Film lubricant (with teflon) for the innards. It works like a charm now. Thanks for the help.Quote from: garrettm on January 31, 2021, 02:22:21 amGood to know the hum is normalish. Thanks for the photos. I did spray down the meter switch with some Deoxit and then again with some of the lubricant as they do tend to get gunked up over the years, although my analog display was working fine.I checked with a scope and the voltage changes look smooth now. Thanks for the tip.

author: 6151kokodef
author_rank: Newbie
timestamp: October 22, 2021, 03:19:27 pm
content: I got a 6115A which is pristine internally, but the 1V and 10V thumbwheel switch ranges would jump wildly to 9V (and 90V!!!) when switching between digits 2-3-4. I bit the bullet and dissected the thumbwheel switches like garrettm. It was quite gunked up as well. I cleaned them with alcohol and they work like new again.As for the transformer hum I guess it's normal. Mains is 220V 50Hz where I am. My 6115A has very little hum but my HP 6228B and relatively modern HP 6632B hum like no tomorrow.

author: Slavko
author_rank: Newbie
timestamp: November 14, 2021, 07:50:33 am
content: I have two power supplies hp6114a and hp6115a and both had the same low frequency hum problem. It turned out that the reason was in the flat yellow capacitor 1mkf 250v. After replacing it with WIMA, the sound disappeared completely.

author: AlpineJoe
author_rank: Newbie
timestamp: December 11, 2023, 11:41:46 pm
content: Resurrecting an old thread, but I now own one of these and need to go through the thumbwheel switches.From the photos, I see that I would trim the plastic that staked the PCB to the housing, then open and clean the wipers and PCB with gold plated traces. What I don't see is any mention of what is done to re-stake the switch back together.Do folks re-heat stake the posts? Use 5 min epoxy? Anything else?Thanks for any tips.

author: coppercone2
author_rank: Super Contributor
timestamp: December 11, 2023, 11:51:21 pm
content: Quote from: Slavko on November 14, 2021, 07:50:33 amsome ceramics they have buzz too. idk if its the new power grid situation or what, because the SLCC capacitors should not age. I replaced them with equal caps and there was still a buzz. I even added RFI filter to it, and it still buzzed.for the switches, I wonder if its possible to build a compression plate thing with some standoffs /long bolts around the entire thing, so you don't need to use any fucking plastics technologies therelike really long thin threaded rods

author: garrettm
author_rank: Frequent Contributor
timestamp: December 12, 2023, 12:05:03 am
content: Quote from: AlpineJoe on December 11, 2023, 11:41:46 pmJust wrap the re-assembled switch stack in kapton tape. That's what I did. This way you can clean the switches again--if needed--by simply removing the tape as opposed to possibly destroying the switch housings by trying to pry apart glued together plastic.

author: coppercone2
author_rank: Super Contributor
timestamp: December 12, 2023, 12:11:05 am
content: good idea, maybe give it 1 layer of self amalgamating tape over it because it wont have a bond failure like kaptonor a giant segment of heat shrink.but what pissed me off about those switches is the spring loaded bits

author: AlpineJoe
author_rank: Newbie
timestamp: November 23, 2024, 05:48:36 am
content: Quote from: garrettm on December 12, 2023, 12:05:03 amFinally decided to work on my 6114A, but already disassembled, cleaned the contacts, and reassembled and used the tiniest dot of uv cure epoxy in the front two corners and two more spots near the rear posts to hold it back in place before I read your reply.Cleaned up the rest of the unit by blowing it out with compressed air and using a dry flux brush. Time to power it back up and see what the next problem is.

author: coppercone2
author_rank: Super Contributor
timestamp: November 23, 2024, 06:43:47 am
content: probobly the switch loland I figured out how to hold it together finally, you can use a zip tie

author: AlpineJoe
author_rank: Newbie
timestamp: November 23, 2024, 10:29:33 pm
content: Powered it up last night and was amazed that it pretty much works - except the output voltage is way off. Dial up 1.00 and I get 1.37V. 10V setting and I get 13.7V. I measured the voltages at the A2 board and the +16V is measuring 22.8V! Okay, need to figure that out.So just my luck, it ends up that R8A is open. Why couldn't it have been one of the easier to replace parts? 15.82K 0.1% 1ppm. Why would this fail. . . .Sifted through my 1/4W resistors and found a combination that gets me close - installed it and my 16V reference is near 16V. Pushbutton settings give me close to what is expected.Now the search for proper replacement.

author: coppercone2
author_rank: Super Contributor
timestamp: November 23, 2024, 10:41:53 pm
content: you can tryhttps://www.heisener.com/ProductDetail/Y000715K8200V0Lgood luckhttps://www.integrated-circuit.com/products-detail/Y000715K8200V0L/EIS-2897594.htmlhttps://www.digikey.com/en/products/detail/stackpole-electronics-inc/RNCF1206TKW15K8/16206097

author: TimFox
author_rank: Super Contributor
timestamp: November 23, 2024, 11:07:15 pm
content: In this type of power supply, the decade switches to program the output voltage form a variable resistor, as part of the DC feedback circuit.Each resistor has a corresponding switch element that shorts it out, or not.If a contact somewhere in the switch is dirty, when that contact is supposed to close (0for that part of the resistor string), the resulting resistance will be too high for the setting, and the output voltage (proportional to the total resistance of the string) will be too high.Therefore, it is important to clean the switch contacts.

author: AlpineJoe
author_rank: Newbie
timestamp: November 24, 2024, 06:46:09 am
content: Quote from: coppercone2 on November 23, 2024, 10:41:53 pmHere's an interesting source. Was recommended this place from the HP test instrument Groups.io page.https://www.texascomponents.com/store/VishayFoilResistors.aspLooks like they can make custom resistors quickly. Not sure the cost but the author didn't think it was exhorbitant.HOLY SMOKES!They will make a custom resistor for about $13.https://webdirect.texascomponents.com/ProductDetails.asp?ProductCode=VSMP%5F1206%5FCUSTOM%5F0%2E010.3W 0.2ppm 0.01% (Any Custom Value from 250 to 25K ohms @ 0.01%)or 1/2W for $16.23https://webdirect.texascomponents.com/ProductDetails.asp?ProductCode=VSMP%5F2010%5FCUSTOM%5F0%2E01VSMP 2010 Bulk Metal (Z) Foil Surface Mount Resistor; (aka Y1627) 0.5 W; 0.2 ppm/C TCR 0.01%Amazing!

author: AlpineJoe
author_rank: Newbie
timestamp: November 27, 2024, 07:40:54 pm
content: Quote from: AlpineJoe on November 24, 2024, 06:46:09 amUnfortunately 'no minimum order' and the fact the form shows I can order 1 pc doesn't mean I can order only 1 pc.I contacted TCC asking what the price with shipping would be and their reply was "The MOQ for the series is 5 pc. since is a very peculiar R value."Not sure why my 'any custom value from 250 to 25K' is special.Meanwhile I can find 5ppm parts of 15K and 820 ohm resistors in stock from Digikey for <$5 shipped, and really I just need to be in the range that A2R5 can adjust for so I could just use a single close value vs hitting 15.82K exactly.

author: coppercone2
author_rank: Super Contributor
timestamp: November 27, 2024, 09:29:15 pm
content: Quote from: AlpineJoe on November 24, 2024, 06:46:09 ami think its cheaper lasers that make this possibleAt some level, a tiny metal paper is just being passed through a laser printerbut it does not have leads on it. I guess you need a litle pCB with some thick copper leads

author: factory
author_rank: Super Contributor
timestamp: November 27, 2024, 09:56:06 pm
content: They do through hole parts for a little more $ too.https://webdirect.texascomponents.com/ProductDetails.asp?ProductCode=Z201%5FCustom%5F0%2E10David