HP 3410A AC Microvoltmeter Restoration ** In operation added** - Page 1
Forum section: electronics / testgear

author: robrenz
author_rank: Super Contributor
timestamp: April 27, 2014, 06:36:08 pm
content: I got this almost a year ago for doing low level AC measurements (original thread here). Its lowest scale is 3µV full scale and 50nV per division. Max is 3V full scale. I bought it mainly to do power supply ripple measurements and to characterize the below spec AC performance of my 8846A. This is a phase locking voltmeter with a tunable frequency range from 5Hz to 600kHz. It seems pretty rare as I have not seen a listing since. I finally got around to restoring it and though I would share some of the process.Manual hereHP Journal article about it(takes a while to load and it is the second article)The only actual electrical repairs it needed were a new incandescent range indicator bulb and the range switches needed cleaned and lubed. It also needed calibration but it basically worked as received. It had been exposed to some type of corrosive situation that is evident in some of the pictures.BeforeAfter, Stickers removed with xylene and Melamine foam sponges (Magic erasers). Main panel was very lightly wet sanded with a very fine sanding sponge (type used for fingernails) just enough to get rid of fine scratches. Then the paint was polished with Mequires PlastX to restore the shine. The metal parts of the two switches were polished with Simichrome applied to a 25mm diameter fabric buff on a flexible shaft. Everything else will be covered belowBeforeSame treatment to the paint of the top rail. Yes those magic sponges are magic, you just have to rub vigorously and not be afraid to use up several whole sponges on a restoration.BeforeAfterAfter, Ahh…. be still my heart!AfterAfterMore to follow….

author: robrenz
author_rank: Super Contributor
timestamp: April 27, 2014, 06:45:50 pm
content: Simichrome was used on all the metal. Fabric buff on the outside and a very hard felt bob with a hole drilled in it to clear the center of the BNC and the OD. turned to a snug fit in the BNC ID. Both used at slow speed in a flexible shaft.BeforeAfterPretty nasty, they used something like clear fingernail polish to seal down the Dymo label to the lid.Label carefully picked off and the clear stuff could also be picked off.After about a quarter of a magic sponge later using citrus based cleaner and IPA. Then a thorough application of “Mothers back to black” to restore the luster to the vinyl.Less drastic situationSuccumbed to the same treatment as aboveA real nightmare, permanent marker on vinyl!I finally ended up using toluene and magic sponges using a light touch. It took quite a while and the Toluene tends to soften the vinyl so be very carefull if you try this. Several applications of back to black brought the vinyl luster back.The bakelite knobs came back to life by polishing with thePlastX(EDIT: Simichrome works even better on the bakelite) using felt buffs, fabric buffs, and natural bristle brushes on a flexible shaft. The white indicators were refilled with new white paint.Frequency dial showing corrosion under the clear seal. The right hand side has the clear sealant removed.Glass bead blast to remove the corrosion and get a uniform satin finish.Graduations filled with epoxy loaded with carbon black. I used a very small hypo needle on my solder paste dispenser unit.When partially cured I used a popsicle stick wet with MEK to rub off the sloppy feather edges of the filling.Whole thing sealed with Permalac. Very expensive but very good stuff for extreme long term durability.More to follow….

author: SeanB
author_rank: Super Contributor
timestamp: April 27, 2014, 06:56:01 pm
content: Another neat restoration there.

author: robrenz
author_rank: Super Contributor
timestamp: April 27, 2014, 07:03:30 pm
content: The meter face was a major concern as it was very yellowed and peeling.Looks like the emusion was affected by whatever the corrosive atmosphere was.This is after I cleaned off what looked like a fine powdery fur over all the metal parts. I used one of those adjustable fiberglass brushes which worked very well at removing it without disturbing the metal. Extremely sensitive parts here, it would be tempting to blow this out with an air duster but that could easily bend/break the movement. I used a soft artist brush to sweep all the debris out.At first I wondered how I was going to replicate the meter face with my camera and keep the scale. And I was thinking I would have to use some photo shop to remove the flaking and fading. Then I read a thread on here about taking pictures of circuit boards with a scanner. That took care of the scaling issue, now I just need to learn how to touch up the image. Then the light bulb went on, set the scanner to one bit mode. That gave a perfect black/white only image that was perfect with no processing needed. Notice the brownish fading on the original on the right.The new face assembled in the meter.The new meter face printed out on Papillo self adhesive photo film (upper left). Meter face plate with the original graphic removed (lower right). Notice chromed surface for when it would be used for a mirrored face. It was very polished but I scuffed it with a sanding sponge for better adhesion. I had to figure out how to get the photo film applied precisely on the meter face plate. The cardboard is about 2mm thick which is slightly thicker than the meter face plate. The two cardboard pieces were cutout together with a window slightly larger than the meter face plate.Double stick tape applied to the perimeter of the opening of one cardboard piece.The protective strip of the double stick is removed and then the cardboard is stuck to the printed side of the sticky photo film. Notice the alignment windows that I cut at the corners so I will be able to see the metal meter face plate through the overlay.The above flipped over and the protective layer of the sticky photo film is removed and the other cardboard piece is stuck down on the sticky side of the film.The metal meter face plate is placed on the table and then the whole cardboard framed photo film unit is carefully aligned over it. The cardboard being slightly thicker than the metal face plate allows precise positioning without sticking until you want it to. When in position I used a piece of the protective backing to press down the film to contact the faceplate. It is very important to press down in a wave from one edge to another to not trap any air bubbles.Flipped over showing the faceplate stuck in proper positionAn Exacto knife trip around the perimeter to free the meter face.Two rubber washers and Nylon screws keep the face plate electrically isolated from the meter mechanics. Notice the stud that gets connected to a ground wire to drain charge of the faceplate that could influence the needle.Aged bakelite and dirt.After a polish with PlastXUsing the 2450 SMU to test the meter at full scale. It is a 100µA meter so not bad being only 4µA off at full scale. The smallest increment that I could see needle response was about 100pAMore to follow…

author: Carrington
author_rank: Super Contributor
timestamp: April 27, 2014, 07:06:39 pm
content: Amazing, looks like new.

author: max-bit
author_rank: Frequent Contributor
timestamp: April 27, 2014, 07:07:32 pm
content: good job !!!

author: robrenz
author_rank: Super Contributor
timestamp: April 27, 2014, 07:11:49 pm
content: One of the foot bars showing the effects of the corrosive atmosphere.Wet sanding all the scratches and dings out. I know… I need help.Fingernail sanding sponges and sanding sticks to clean up all the surfaces and edgesPlastX, hard and soft felt buffs, fabric buff and flexible shaft to polish the plastic. This is a flexible plastic so it took quite a while to get the right pressure speed technique combination to get a good finish. (I warned you)Before top, after bottomCorrosion on the side framesNothing a trip to the glass bead cabinet can’t cure.Refinishing all the polished edges of the frames. This is a cast iron surface plate with 240 grit silicon carbide paper lightly contact cemented in place with 3M77 spray. You could use a piece of tempered glass to do the same thing. First the face and all 4 edges are sanded until they clean up completely. All the edges are filed to have a uniform edge break. I used sanding sticks with 320, 400 and 600 grits before polishing with Simichrome on a hard felt buff in the flexible shaft.Edges before.Edges after.Homemade sanding stick method. Lay out craft store popsicle sticks and the silicon carbide paper on some scrap cardboard and lightly spray with the 3M77 spray contact cement. Stay far enough away that you don’t blow the sticks and paper away!Give the glue some time flash off and flip the paper over onto the sticks and press down to bond. Put this on a cutting board and trim both edges right next to the stick to separate them.Very handy and inexpensive.More to follow…

author: PedroDaGr8
author_rank: Super Contributor
timestamp: April 27, 2014, 07:23:43 pm
content: Just when I don't think you can impress me any more. You do it again. Truly impressive, that must be how it looked RIGHT when it came off the factory line.How are you liking the Mothers Back To Black? I remember I recommended that to you in the 6114A restoration thread. The buttons on my 6114A are still as black and shiny as the day I applied it.

author: robrenz
author_rank: Super Contributor
timestamp: April 27, 2014, 07:25:48 pm
content: Left side. That circuit board is the input section and has a full cover that is not in place.Right side.BottomTop.Frequency setting potentiometers. Notice the shielded conductors on the last two ganged pots.Front panel removed and everything hanging in the breeze.The A4 circuit boardThe A3 circuit boardThe A2 circuit boardThe A1 circuit boardThe switches were treated with Deoxit D100L and cycled thoroughly. Then washed with electronic cleaner spray and blown out with compressed air. This shows final application of Deoxit G100L to lube then thoroughly cycled and blowing off any excess.This is the cover plate that is behind the frequency dial. It was originaly contact cemented to the bakelite frame. It had to be removed to get to the screws that hold the body of the dial reduction unit. So I punched two holes where the screws are so the plate could remain permanently. The corner pads are 3M high strength adhesive. The extra thickness was not a problem as the dial was pretty far away to begin with.I have done an initial full calibration and the performance is impressive but I will save that for another thread.

author: david77
author_rank: Frequent Contributor
timestamp: April 27, 2014, 07:35:56 pm
content: It is truly impressive to see how you get all these old and well-used pieces of gear to look as good or maybe even better as the day they were produced. I wish I had the patience and experience to do that.Can you tell how many hours you invested in this restoration?

author: SeanB
author_rank: Super Contributor
timestamp: April 27, 2014, 08:08:43 pm
content: Very nice. I coud not afford a surface block, so I use a granite floor tile that is attached to a plywood backing with flexible polyurethane, which is pretty close to being optically flat.On those boards I would suggest looking at the seals of those Sprague capacitors and looking for a white discolouration on the red rubber ( regular electrolytic ) or green rubber ( wet slug tantalum capacitor) end seals. If they are faded with the white film then the seal has degraded, and you probably would need to replace them. If not then simply check each in circuit ( first rough approximation to say if it is nailed to the perch or is still squawking) for ESR, and then decide if you want to replace the still usable ones.

author: Vgkid
author_rank: Super Contributor
timestamp: April 27, 2014, 09:49:00 pm
content: Very good job on the resoration. Does the meter use thermal, or diode based rms conversion.

author: fpliuzzi
author_rank: Regular Contributor
timestamp: April 28, 2014, 12:02:01 am
content: Spectacular restoration indeed. Bill Hewlett and Dave Packard would have been touched by the level of respect you've shown to this formerly crusty 3410A. Your craftsmanship is inspiring.Regards

author: Vgkid
author_rank: Super Contributor
timestamp: April 28, 2014, 12:22:26 am
content: I just answered my own question, it utilizes a pll to lock the frequency. Then takes the vpp vals and determines the vrms value.

author: robrenz
author_rank: Super Contributor
timestamp: April 28, 2014, 12:37:42 am
content: Quote from: Vgkid on April 28, 2014, 12:22:26 amIts uses the filtered output of a synchronous rectifier that is basically average responding not really true RMS.The HP Journal link above has a very good discussion about it.

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2014, 12:41:09 am
content: Top notch work!

author: robrenz
author_rank: Super Contributor
timestamp: April 28, 2014, 12:43:24 am
content: Thanks everyone for the very kind words.@PedroDaGr8 Thanks for that tip, the Back to Black is far superior to Armor All.@David77 Approximately 30 hours.@SeanB Thanks I will check those caps.

author: Unknown
author_rank: Unknown
timestamp: April 28, 2014, 12:53:51 am
content: Verynice job! And an interesting unit; I've got to get myself one of those.Yes, the Mother's stuff is a nice very light cut and polish that beats the pants off ArmorAll. Come to think of it, does anyone know what the hell ArmorAll is good for?

author: lowimpedance
author_rank: Super Contributor
timestamp: April 28, 2014, 01:03:16 am
content: Yet again a truly magnificent restoration, Are you game to actually use it now.I particularly liked the BNC restoration, learned something that will come in handy.

author: Vgkid
author_rank: Super Contributor
timestamp: April 28, 2014, 01:55:26 am
content: Quote from: robrenz on April 28, 2014, 12:37:42 amThere is nothing wrong with using average measurements, its not like this is for super accurate measurements. Though avg responding meters can be rather accurate.

author: han
author_rank: Frequent Contributor
timestamp: April 28, 2014, 03:30:46 am
content: Amazing. That truly an restoration art

author: quarks
author_rank: Frequent Contributor
timestamp: April 28, 2014, 03:35:40 am
content: Great work

author: BravoV
author_rank: Super Contributor
timestamp: April 28, 2014, 03:44:11 am
content: Thank you Robrenz, amazing restoration works and also appreciate the documentation efforts as well.Also learned useful tricks, especially on cleaning the bnc connector, btw since Simichrome is not available locally here, does Autosol has similar performance for this kind of job ?

author: calexanian
author_rank: Super Contributor
timestamp: April 28, 2014, 05:56:36 am
content: Looking good!

author: HKJ
author_rank: Super Contributor
timestamp: April 28, 2014, 06:10:31 am
content: Quote from: Vgkid on April 28, 2014, 01:55:26 amThe difference between average and rms are not that great when the meter is tuned to a single frequency

author: quarks
author_rank: Frequent Contributor
timestamp: April 28, 2014, 09:52:33 am
content: Hello robrenz,sorry for getting OT, but may I ask for a hint how you would clean and bring back the "black print" on keys like in the picture.Thanksquarks

author: SeanB
author_rank: Super Contributor
timestamp: April 28, 2014, 09:59:03 am
content: Nothing you can do there as those are screen printed onto the keys. Either you engrave the legends into the keys or you reprint using a screen and ink. Better keys use a 2 shot injection moulding that makes the contrasting colour that extends down through the key top.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 28, 2014, 09:22:21 pm
content: Hi robrenz,you've done a great job, I really admire that!Additionally, you present here a whole bunch of cleaning tricks.The old, stinky and sticky HP plastic surfaces always need some facelift.Maybe I rework my old gear after your presentation..Frank

author: plesa
author_rank: Frequent Contributor
timestamp: April 28, 2014, 09:31:49 pm
content: Wauu, thats awesome. Really nice work!!! It will just needs to add smell of new instrument

author: ecat
author_rank: Frequent Contributor
timestamp: April 28, 2014, 09:49:10 pm
content: A thing of great beauty robrenz, excellent work.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 29, 2014, 01:13:57 am
content: Making my own epoxy paint to fill recessed engravings is something I wouldn't have thought of. Noted and remembered, thank you for sharing.

author: dannyf
author_rank: Super Contributor
timestamp: April 29, 2014, 01:18:39 am
content: QuoteNicely done.

author: robrenz
author_rank: Super Contributor
timestamp: April 29, 2014, 01:22:29 pm
content: Thanks again all for appreciating this restoration. Its great that there are some techniques that you are finding useful.@ lowimpedance Yes I will be using it. A video should follow@BravoV The Autosol looks like it may be similar and probably work even though it is targeted at Aluminum.@quarks I would probably have a silk screen made and redo the keys like SeanB mentioned.@Dr.Frank Glad it inspired you, (don't forget to take the before and after pictures)

author: BravoV
author_rank: Super Contributor
timestamp: April 29, 2014, 03:36:55 pm
content: Quote from: robrenz on April 29, 2014, 01:22:29 pmThanks, and other question on using the rotary fabric buff with this kind of paste when used at the bnc connector surface.I know you've mentioned the words "slow speed", its just sometimes I'm so worry at this process, it may eat off the outer chrome (or is it nickel ?) plating too much, and will starting to expose the inner yellowish brass base metal, that will be my nightmare.Just stop when it is enough bling/shine ? or I'm just worrying this way too much ?Also once finished buffing, did you apply any extra coating at these metal surface to protect it ?Hope I'm not bugging you too much.

author: robrenz
author_rank: Super Contributor
timestamp: April 29, 2014, 06:48:59 pm
content: You are not bugging me, I am glad to help where I can.You could test/practice on a cheap adapter first so you don't toast your favorite instruments BNC. Simichrome is an extremely fine polish and would take quite a while to buff through the plating. Simichrome is made in Germany so I would think you should be able to get it somewhere. Simichrome leaves a protective coating so I did not apply anything else. it only takes a about 3-5 seconds of buffing to get that shine. Other metal polishes may be more aggressive so you should test first.

author: simonmc
author_rank: Contributor
timestamp: April 29, 2014, 09:23:14 pm
content: I showed this thread to my daughter. As she was in the workshop with me 'learning', she pointed to my hp5326b frequency counter and said 'We have to do that to THAT, dad'. To be honest i had to agree. If it comes out half as good as your restoration then i will be pleased, and the project will give me some father daughter time..

author: robrenz
author_rank: Super Contributor
timestamp: April 30, 2014, 02:20:15 pm
content: Glad it inspired you. I get a lot of satisfaction bringing these things back to life,

author: robrenz
author_rank: Super Contributor
timestamp: May 17, 2014, 07:35:45 pm
content: Here is a quick test using the 3410A to measure the AC rms ripple at 60Hz, 120Hz, 180Hz, and 240Hz. PD2005 set at 10V and about 475mA (almost max current) The 87 is reading the oscillator output of the 3410A. The values were about the same at 20V output and decreased about 25% at 1V60Hz about 20µV rms120Hz about 40µV rms180Hz about 49µV rms240Hz about 25µV rms

author: robrenz
author_rank: Super Contributor
timestamp: May 18, 2014, 02:50:58 pm
content: I forgot about ground loop voltages at these levels. The manual actually tells you to float the meter when using the very lowest ranges. So I made a ground lead interrupter out of junk bin parts with a line switch on the ground lead only so it can be floated or not with the switch. This allows the meter to be grounded while safely making connections and adjustments then disconnect the ground only to take a reading. There was only this much difference at 60Hz, 120Hz and 180Hz had no change in reading when floated.60 Hz reading of 25µV rms with the ground connected.60 Hz reading of 5µV rms with the ground disconnected.

author: SArepairman
author_rank: Frequent Contributor
timestamp: May 18, 2014, 06:08:16 pm
content: now you just need to compare it to a DSA

author: robrenz
author_rank: Super Contributor
timestamp: May 18, 2014, 06:16:38 pm
content: I would love to, please send me one and I will do the testing

author: HighVoltage
author_rank: Super Contributor
timestamp: May 18, 2014, 06:42:19 pm
content: This is truly inspiring and I learned a lot, by reading your steps.If I would have only looked at the "before" pictures, I would not have believed that such a restoration is possible.Amazing.Thanks for sharing.

author: FrankenPC
author_rank: Unknown
timestamp: May 19, 2014, 04:56:42 am
content: Any tips on removing dings and dents from the cover panels?

author: robrenz
author_rank: Super Contributor
timestamp: May 19, 2014, 11:34:13 am
content: Concave side of dent down on flat compliant surface like a piece of rubber sheet on top of a rigid flat surface. then use a large radius body hammer gently on the convex side of the dent. If you only have regular hammers place a piece of scrap sheet metal over the dent to spread the force of the hammer blows over a larger area and not leave smaller hammer dents. The compliant surface allows the hammer to slightly over bend which is necessary to get a flat surface.

author: saturation
author_rank: Super Contributor
timestamp: May 20, 2014, 12:19:19 pm
content: Incredible work and documentation.A model for everyone!

author: bsgd
author_rank: Regular Contributor
timestamp: May 20, 2014, 07:16:31 pm
content: A-M-A-Z-I-N-GThank you for sharing!

author: robrenz
author_rank: Super Contributor
timestamp: May 21, 2014, 06:45:11 pm
content: Thanks again all.@ saturation, glad to see you are still around

author: TheRuler8510
author_rank: Regular Contributor
timestamp: June 17, 2014, 02:44:00 am
content: Quote from: robrenz on May 21, 2014, 06:45:11 pmrobrenz or anyone else,Where can a guy buy toluene by the ounce? The only way I can find it on-line or in Home Depot is by the gallon.Any Ideas?Thanks,

author: PedroDaGr8
author_rank: Super Contributor
timestamp: June 17, 2014, 06:07:37 am
content: Quote from: TheRuler8510 on June 17, 2014, 02:44:00 amHonestly, it's pretty low priced. The price at the one liter volumes is low enough a liter should be fine. You would be hard pressed to find a smaller volume for much cheaper. Part of the problem is the shipping restrictions.

author: saturation
author_rank: Super Contributor
timestamp: June 17, 2014, 11:07:25 am
content: my pleasure, and your restorations have few peers.Quote from: robrenz on May 21, 2014, 06:45:11 pm

author: robrenz
author_rank: Super Contributor
timestamp: June 17, 2014, 12:37:51 pm
content: Quote from: TheRuler8510 on June 17, 2014, 02:44:00 amIf you are getting the Toluene based on it getting the permanent marker off the vinyl coated covers as shown in this restoration be warned.It is no magic bulletand it doesn't just remove the marker and leave undamaged vinyl behind. It takes an extreme amount of care, technique and patience to get what was shown here. AND it does not work on all vinyl as it does not work on Power Designs PS vinyl it dissolves the vinyl too quickly. I just don't want you spending a lot of money on a gallon because of my recommendation and possibly be very disappointed.

author: TheRuler8510
author_rank: Regular Contributor
timestamp: June 17, 2014, 10:49:48 pm
content: Quote from: robrenz on June 17, 2014, 12:37:51 pmUnderstood, Thanks!

author: Wessneroo
author_rank: Newbie
timestamp: July 23, 2014, 03:49:57 pm
content: Any recommendations for a solution to refinish the frequency dial for someone who doesn't have access to bead blasting? Great restoration, thanks for sharing!

author: robrenz
author_rank: Super Contributor
timestamp: July 23, 2014, 05:12:29 pm
content: Most automotive machine shops have a glass bead unit. I am sure most would blast a dial for you for a cup of coffee or a beer. There is nothing else I know of that gives that type of finish. If they give you a choice you want to use finer glass bead size and around 40 psi.

author: Joule Thief
author_rank: Regular Contributor
timestamp: July 24, 2014, 11:45:24 am
content: If you have a small air compressor at home, you may want to try a home-made "soda" blaster. Think air gun shooting out baking soda. I use this combo to clean carburetors in lawn and garden equipment. After blasting the carb, a soak in water dissolves the left over baking soda. The finish on the metal is very similar to bead blasting. YouTube has several videos on home made soda blasters.

author: idpromnut
author_rank: Unknown
timestamp: July 24, 2014, 01:36:50 pm
content: @robrez: Wow, I am absolutely blown away by the restorations you've done. Thanks for sharing!

author: mmagin
author_rank: Frequent Contributor
timestamp: April 19, 2016, 08:17:17 pm
content: Quote from: robrenz on April 27, 2014, 06:45:50 pmThe results are beautiful, but is there cause for concern that this may drive particles of metal or polishing agent into the soft teflon, affecting its electrical properties?I've always been too chicken to use more than some isopropanol and a swab on RF or high-impedance connectors.

author: Priestblood
author_rank: Contributor
timestamp: May 28, 2016, 05:35:46 pm
content: Excellent restoration top class .Very nice to see how you did it .what was the hardest part to do.RegardsWayne