Free Abandoned HP 3478A 5-½ Digit DVM Repair

We repair a classic HP 3478A 5-½ digit voltmeter, and admire its ultra complicated A to D converter.
HP Multislope II ADC patent: patents.google...
Ian Scott Johnston video on HP 3457 backlight mod: • No.042 - HP3457A Backl...
Blacklight display mod: www.eevblog.co...
LCD protocol reverse engineering: www.eevblog.co...
OLED mod: www.eevblog.co...
Ken Shirriff's Nanoprocessor reverse engineering: www.righto.com/...
Ken Shirriff’s reverse engineering of the hybrid in Marco Reps’ HP 3458: x.com/kenshirr...
Jeff Peletz amazing HP instrument pictures: hparchive.com/w...
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"Elevator Music" Credit: Crinoline Dreams by Kevin MacLeod
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[@sebastian_harnisch]

You can also read our the calibration data via HPIB and restore it after the battery replacement. That is what I did, except after powering it on it still had the calibration data as if I hadn’t disconnected the battery.

[@CuriousMarc]

Thanks for the tip, I did not know! Worth a pin. [Edit:] No wonder I didn't know, it's a hidden HP-IB command! Details here: www.eevblog.com/forum/repair/hp-3478a-how-to-readwrite-cal-sram/

[@geoffreykeane4072]

Never change your theme music Marc

[@reklrekl]

whats the thteme music acutially called? tried to "shazam" it, but couldn't find it. Thanks!

[@IanScottJohnston]

Oh! very pleased to see a mention regarding my 3457A backlighting mods……thanks!

[@leppie]

Oh hi, Iron! :D

[@andymouse]

Iron 'Bru' Scottjohnston howdy !!

[@dieSpinnt]

Great work!:)

[@KaldekBoch]

Is it weird I find myself bopping to the intro music? Ba-da-ba-da-bap-bap-daaaa-daaa

[@shawnhuk]

Nope! I do it evvvvery time!!

[@chrisdooley1184]

I watched this PBS (local) show about restaurants and specifically diners in the eastern half of Pennsylvania and the music used was exactly this. No wonder I find myself thinking about homemade cinnamon rolls with pecans and giant omelettes 😂.

[@xephon3000]

Not weird at all! I do too! The intro and outro are certified bops!

[@TheGunnarRoxen]

me too

[@almostanengineer]

Nope, I also find every time BigClive say’s ‘one moment please’ I make an audible ‘boop’ type sound 😅

[@Runco990]

I love the explanations with elevator music. After 40 years of doing electronics, I STILL learn something. 👍

[@Woffy.]

Only on this channel will you hear " It's too bad this instrument isn't broken enough " . A joy to hear their technical converstion without ego's.

[@bradleystach6275]

"Puts modern Keysight to shame" Guess Marc is not looking for a sponsorship. 🙂

[@ttyR265]

Or he's just honest and figures Keysight would agree with him.

[@meJaso]

Truth hurts sometimes

[@SeanBZA]

He already is sponsored by them, and likely they can no longer make the old instruments any more, having sold off the fab they had that was able to do all the precision semiconductors and the hybrid parts they used for them.

[@thesteelrodent1796]

@@SeanBZA they could make their new instruments to the same level of quality as the old, but the problem with running a business is that you don't make any money if you make your products to last forever

[@CuriousMarc]

Part of it is that the economics don't work out anymore. The electronics are so cheap that it does not make economical sense to surround them with expensive mechanical design and switches. Also, all the nice front panel experience has been replaced by user interface software, and the software interface part is not up to par, even on the very expensive instruments. No good excuse for that.

Thanks for the great video. One of the analog designers on the HP 3478A, George Hnatiuk, was pretty active on the HP-Agilent-Keysight forum until a couple of years ago. I had a lengthy phone conversation with him about repairing one of my 3478A's. Sadly, his house later burned down, and less than a year later he passed away. A very bright person!

[@pomonabill220]

It is so sad to hear that one of the genius engineers at HP has passed. What a gold mine of knowledge he had!

[@d.jeffdionne]

I have a real soft spot for the 3468A and B. 68s use a discrete zener reference, and you'd think they would drift or have a poor tempco... but after all these years things have generally stopped moving, and they have pretty legendary stability. At least on the units I have. The 78A and the 57A both use the same A/D converter, and the LM399 reference. These things are absolute works of art... with the 3457A giving 7 1/2 digits from (more or less) the same A/D circuits :)

[@SeanBZA]

So long as you do not reset the aging by removing it, it will be stable for decades.

[@ferrumignis]

Is the zener heated on the 68 models?

[@d.jeffdionne]

@@ferrumignis No, the zener reference in the 3468 isn't heated. I wondered how closely they had nulled out the temperature coefficient, and just recently got a data point... I left a Vishay VHP101 10k resistor (claimed zero tempco) connected to an HP3468B for about a week, exposed to temperature and humidity variations. The reading never changed, not even in the least significant digit. So, to within 10ppm the HP tracks it.

[@ferrumignis]

@@d.jeffdionne That's amazingly good for a compensated zener, HP never fails to impress me.

[@Powertampa]

If I had had a teacher like you I probably would not be so afraid of electronics nowadays.

[@parkerlreed]

When you trust the HP so implicitly that you come to the realization your decade box might not be spot on! Love it.

[@W6EL]

Agree completely about those dim LCDs. For a bench meter, readability is the point! I’m happy to sacrifice a digit if I can actually read it among the solder and electrolytic capacitors smoke… Fluke 8505A and HP 3490A (with added RMS module) here. Bright red LEDs. Can’t miss em.

[@terrygood2782]

Yes, I love the display on my HP 3490A, too.

[@JCBudro16]

How fortunate that marc would put out this video a day after I acquired one of these for measurement automation!

[@wtmayhew]

My favorite meter oddity is a Digitec four digit DC mechanical bench meter which I rescued from the scrap pile at NASA Lewis back in the 1980s. There are four ranges of 1, 10, 100 and 1000 Volts. Mechanical? Yes. The readout is like the odometer on an old automobile, driven by an AC motor and also connected to a wire wound variable resistor. The input is connected to one leg of a Wheatstone bridge and the opposite leg is connected to the wiper of the variable resistor. When the bridge is in balance, the input burden is very small, so high precision is possible. The bridge balance is read by a mechanical chopper stabilized transistor amplifier whose output drives shading coils on the motor to provide feedback tending to move the variable resistor to bring the bridge into balance. There was a matching AC to DC converter box, but I parted company with that somewhere over the years. I still use this approximately 60 year old meter for adjusting bias pots on audio amps. The least significant digit has 200 microvolt hash marks between the major digits. The least significant digit is analog like the least significant digit on an automobile odometer, so it is really easy to hone in on a bias adjustment. It is much easier than using an electronic digital meter. The Digitec must be a pretty rare bird, as I just did a cursory Google image search and I got were Digitec electronic panel meters. There aren’t any listed on eBay either.

[@wtmayhew]

Ninja’ed by KZbin. I found 41 second video of a Digitec Model 201 which was uploaded ten years ago, here: m.kzbin.info/www/bejne/rp2QhJ2LjJ6IntE My unit has a NASA calibration sticker with a note “repaired” 8-3-67.

[@CuriousMarc]

I think youtube ate your reply, but here is the video you linked: kzbin.info/www/bejne/rp2QhJ2LjJ6IntE . I’m quite impressed by how fast it is. Great instrument indeed!

[@erikdenhouter]

@@CuriousMarcKZbin should be swallowed by its own algorithm's. Thanks for the link.

[@DoRullings]

I get happy like a little kid when I'm notified about a new CuriousMarc video. This is the best channel when it comes to electronics as you take your time to give very good and detailed explanations about how things work. Thank you!

[@DrFrank-xj9bc]

Nice repair, thank you for sharing. Again, it's the infamous front/rear switch problem, like > 20yo 34401A and even 3458A. That's been discussed and repaired on eevblog as well. I've found out, that a thin film of supposed plasticizer from the switch case had outgassed onto the springy contacts and the inner contacts, and I cleaned it the very same way as you did. That reminded me of the old Fluke 332B/AF I once had, where all the cables got extremely sticky. Coming back to APOLLO, I once visited the Air and Space Smithsonian museum in Washington, where Neil Armstrongs Space Suit is on display, under a glass housing. If I remember correctly, the description noted the very same problem, i.e. deterioration of the suit, due to the plasticizer outgassing.I don't know, how they preserve the suit from further degradation. Same worries about the WASA in Stockholm. O yes, there's really an interesting article about the conservation of Armstrongs suit since 2015!

[@carldaniel6510]

Great video! In this rare case, the problem turned out to be exactly what I thought it was from the start - an open circuit. Amazing work by HP back in the day to come up with that multi-slope A/D design - as you said, someone thought long and hard about that. The truly heroic backlight conversions that you showed at the end - OMG! The OLED display replacement is off the hook!

[@osgeld]

I got my 3478A off ebay back in 2015 as a birthday present to myself. I paid 58 bucks if I recall correctly, and it came from a Boeing facility and had been freshly calibrated according to the label (was good for 2 years yay). It could have a couple extra features on it but overall I love it

[@nikmilosevic1696]

Another 3478A back in business ,nice. I really like these meters. If I see one on ebay for cheap, I am compelled to buy it and fix it.... :D PS: wow never seen one with a bad switch connection, seen bad relays, bad opamp, many bad batteries and capacitors, but a switch, wow.

[@physicshypernova2083]

I used a few older HP devices during my research for my physics PhD. I mainly used the HP-8770a arbitrary wave generators to create laser pulses in experiments with a BEC (Bose-Einstein Condensate).

[@TheGunnarRoxen]

I understand very little but each video I learn one or two new things and I love that. Engineering is fascinating

[@byterock]

Rats you got to the HP3450 before I had a chance to get mine fully working 😉. Nice to see you explanation on the Dual slope I guess I will have cut down on the 'Circuit Talk' part of my video and just put a link to here😊

[@petereggimann]

Interestingly, the Keithley 175/175A and other devices from this series use the same mechanism for A/D conversion. Its function is well described in Keithleys service manual. I had one of those for repairs on my bench last week and it took me some time to figure out, how the conversation is done. So enjoyed your explanation how the convesion works.

[@rhythmhappenings3578]

The Eternacell haunts me.💀 Also, an eternity according to the one in my 3478a was 23 years.

[@North49Radio]

Marc, you and the fellas need to give NASA a hand with Voyager 1. If anyone can help, it's you guys. Thanks again for another video.

[@tyrueiI]

Now see what you’ve done! I had to make an offer for an HP 3468a on eBay. Thanks for all the great videos and chances to learn from you!

[@RicoD5]

I never cease to be amazed by the geniuses that invented such gorgeous electronics

[@jeffm2787]

I've still got a working 3478A. Amazing how stable these things are.

[@InssiAjaton]

Reminded me of what the competitor did - if I remember, Fluke had their own solution, which they called Re-circulating Remainder system. I never have had a reason to really compare the thermal and long term performance of the two, although I have for years owned some Fluke meters, as well as a couple HPs. Well, actually my latest one is a Keysight 34411. And as many times as I run a quick “Round Robin” test between all of my meters - many from the 1980’s - I can only admire, how all of them are still unsure only about their very last digit. I have not used my hat for ages, but would need to raise it for the designers in these two companies.

[@wtmayhew]

I’ve got a Fluke 8060A meter which I bought back in 1983. It was back to Fluke in the late 1980s for a repair when the display CPU quit working. It is my daily driver tool bag meter and hasn’t been recalibrated since Fluke did the repair. I compared the 8060A against my Keysight 34460A 6.5 digit bench meter and they agreed within +/- one or two counts on DC and 60 Hz AC sinusoidal input at 50% scale on the Fluke’s ranges. It blew me away that a field use meter not getting special care had stayed on the mark after 30+ years of use. Keysight rates the DC performance of the 34460A at 75 PPM after suitable warm-up of the internal reference. My guess is the 34460A probably beats that spec for most circumstances.

[@davidv1289]

Great repair! As soon as I saw the wandering display I knew it was an open input but I have never seen the front/rear switch fail. Future video suggestion for an HP multimeter lover - find a broken HP 3490A to fix and analyze. Very interesting digital meter with no microprocessor. Regards, David

[@geoffbarton5917]

I love all those classic HP instrument. Especially after so many years of using and programming them. Such works of art. Keep up the good work Marc. I always watch your videos as soon as they come out.

[@EdwinSteiner]

This channel has inundated me with an irrational fondness for elevator music.

[@mikeiver]

I have one of these on the bench, it was given to me out of a warehouse of stuff at a tech company before it all went to auction. Still works perfectly. I do keep it powered as it has the original battery. I just have been to lazy to do the battery swap. I power the Metcal iron with an isolation transformer rather than using a butane iron for working hot.

[@jlwilliams]

A relatively simple but very satisfying repair. I love it when we get an explanation of how everything works, but the problem turns out to be something that can be solved by DeOxit!

[@wtmayhew]

DeoxIT to the rescue! I’ve been using Caig Labs’ cleaner and preservative since back in the day when it used to be Cramolin blue and Cramolin red. I used it to clean the Deutsch connectors on the inputs of Grass EEG amplifiers in a neurophysiology lab. That and graphite impregnated double shielded coaxial cables let us get clean recordings.

[@pomonabill220]

How LUCKY that it was the front/back switch! I have one of those also and if mine fails, that is the first thing I will look at. I have replaced the 3V battery in mine when I received it just to be sure.

[@KeritechElectronics]

What a nice meter, and indeed complicated - I'm still impressed seeing you go through complex circuits and systems both electronic and mechanical like a knife goes through warm butter. And I love the display mods. This meter seriously deserves a VFD instead of this bland non-backlit LCD. Pesky little Isostat buggers! That's how those multi-section pushbutton switches were called here, very popular through the '70s and '80s. "A thing of butane is a joy for ever."

[@stevenspmd]

I both replaced the battery and caps in my 3478a a few days back. Having a usb-to-gpib converter to download the firmware made things easier.

[@mikedfgfj]

Which one do you used? Prices for GPIB stuff still sky high somehow... I would also like to download the firmware and recalibrate one day.

[@mikedfgfj]

Never though I will be proud making coming-out on the internet that I picked my 3478A from the trash bin. New caps and battery definitely extended the lifetime of the instrument to infinity but backlight mod is also what my hands are scratching about. Would be cool to have a clean mod kit despite google is full of DIY conversions powered by 5V rail.

[@624Dudley]

Interesting 🧐. The dwell time of my mind-blown state has been increased. Good stuff, gentlemen! 👍

[@fenugrec5697]

bleh, YT auto-deletes comments with URLs in them... Attempt 2 : Nicely done ! About the offset in ohms range, note that there is only one set of cal constants; Cal labs seem to favour 4W mode on the rear connectors. Using any other configuration like the more common 2W mode on front terminals, will show noticeable offsets on the lower ohms ranges. To 'offset' this, I patched the firmware to add a "Relative mode". I can't link to it, but it's on github, eevblog, and my YT channel.

[@TangoLima58]

The HP3478 has four or five RIFA filtering caps around the transformer that are always cracked. It may be a good idea to replace them.

[@CuriousMarc]

Nah. We leave all dodgy caps in there for future excitement.

[@Brice23]

I can't claim to know a darn thing about these devices or how the circuitry functions but I sure can say I like to watch you guys working on them. I listen to your analysis and I nod and I reckon I can't be the only guy around here who just likes to be impressed by smart people working on complex devices.. Well, unless all of you guys are engineers as well.. *staring at the floor* :D

[@iamdarkyoshi]

Would love to see a future video adding a backlight or OLED display. I've done backlight mods when I was younger, including adding backlight to the original kill-a-watt meter.

[@saulomoura9402]

HP is simply fantastic! I think is the dream of all people that enjoy electronic.

[@FreqBand]

I light the readout with a short strip of "side emitting" LEDs. These are mounted on the exterior, on a strip of plastic and powered by a small separate PSU.

[@wtmayhew]

The entry level Keysight meter is the34460A 6.5 digit meter is capable of 300 readings a second and it is as nicely made on the old HP equipment. Actually it is probably a cleaner design in some aspects. The 34360A sticker price is about the same as a 1983 HP 6.5 digit meter, so adjusted for inflation it is about 75% less expensive. The 34460A is one of the few items on my bench which I bought new, but I wanted a unit with a traceable calibration certificate.

[@fredlotte5897]

Love the videos. I share your passion for old HP equipment (& Fluke & Tektronix) I hope you checked for RIFA capacitors at the line input. Also, when I replaced the battery on my 2 3478's, I wrote the date on the back of the unit. BTW, according to the April 1981 HP Journal, Mullti-Slope II was developed for the HP3456A.

[@davidboettcher1900]

Who were the people who designed these? I don't mean just HP, it would be great to know, and if possible meet, the brains behind the circuits. Another great video Marc and crew, great job, well done.

[@carstenellwart3315]

George Hnatiuk - designed the ohms current source and the layout of the input resistor circuits. Kelly Wright - designed the dc signal conditioning and the custom input CMOS. Ron Swerlein - designed the ac signal conditioning and rms converter. Gerry Raak - designed the power supply, battery option and LCD. Wayne Oeke - worked on the electrical robustness and AD converter linearity. Bill Miner - mechanical design of the 3468A. Doug Olsen - mechanical design of the 3468B. Gary Staedele - I/O software and hardware design. Jon Pennington - industrial design Ron Tuttle - project manager for 3478A. Rich Wilson - electrical design for the 3478A Virgil Leenerts - electrical design for the 3478A Ed Pennington - mechanical design for the 3478A Ted Crawford - industrial design for the 3478A Norm Dillman - design for the environmental test system and writer of the test software Si Sanders - materials engineer Joe Marriott - section manager for project completion Roy Barker - origina section manager (source: HP Journal 02/1983) hp41.betapersei.com/files/HP%20Journal/HP%20Journal%201983%20Feb.pdf

[@qzorn4440]

Very nice video. Four wires is great for ISO calibration data. 😎 Thank you.

[@TheMovieCreator]

I once got a broken HP 3456A for free, and besides the bit-rot of the Mostek ROMs, the only thing wrong with it was a thin layer of oily substance on one of the bridge connector going between the two sides of the inboard section. Like the problem you faced here, it was practically impossible to see with the naked eye, everything gold plated and no corrosion, it even felt like there was sufficient friction on the connector itself. Only way to spot it was to take a swab to it after realizing it was there one of the control lines did not pass signal.

[@Zerbey]

Great, now you have me researching online auction sites to buy one of these!

[@petermikus2363]

What do you think about the HP 3490A i can find barely anything about them other than the manual.

[@jimmy2drinks]

Good work! I would like to hear more about the MOADRBs

[@originalmianos]

I have one of these with the same issue. I am wondering if I can pull the switch apart without desoldering it?

[@CuriousMarc]

Now that we know how to remove the plunger, that might be entirely possible.

[@originalmianos]

@@CuriousMarc I just had a look at mine today. Two of the connections are open circuit. I unclipped the wire and lifted the tab and it came out. The contacts are shiny and gold like new. No coating on the surface likes yours, even under the microscope, but ... two of the springs are missing from the open circuit bars. :( 1.9 x 3.72 mm. Now to find something that works. At least they don't seem to need insane precision.

[@CuriousMarc]

@@originalmianos Great to hear! I would still wipe the contacts clean. Mine looked new and shiny under the microscope too, but somehow were not making contact.

[@originalmianos]

@@CuriousMarc I got some springs on ebay that were very close but a little longer. (The same wire width and diameter). I lost one of the new ones when I was inspecting it after trimming it. Insane, small parts that are springy. Anyway, as you advised I gave the contacts a bit more of a rub with some cotton and contact cleaner again. Once I got it back together it's all working. I just gave it a quick test and it's well within spec, on the DC voltage range, so it has not lost the calibration due to a battery change by someone else. I have one bit of advice on the assembly. Disconnect the sub-panel the switch is on and turn it upside down when inserting the switch assembly (remembering to put the large spring on first). It's much easier to do without losing springs (which was quite probably what the previous owner did).

[@CuriousMarc]

@@originalmianos Thanks for the note and congrats on your repair! One more HP instrument saved.

[@malcolmgibson6288]

Crumpets, coffee, and curious Marc, a great breakfast.

[@numlockkilla]

Really great repair. Thanks for your time.

[@tartanpion8643]

thank you very much marc, you and your fellows make an awesome and funn work. thank you for sharing that. It allows a mind opening for electronic technician i am. I learn so many diagnosis methods. thank you.

[@engmcgill]

Marc, your timing is amazing! I'm currently trying to repair an Agilent E3634A power supply, which outputs power but voltage and current aren't displayed correctly on the front panel. I'm suspecting the A/D converter, which uses the new, improved Multislope III method. I've been struggling to understand how it works and your explanation has helped me a lot. Thanks!

[@CuriousMarc]

What, they made a Multislope III? You can’t stop these guys. Good luck on your repair!

[@Dukey8668]

My solution for the LCD problem on my 3468 is terrible but it works. A small bracket on the front of the instrument holds a section of LED strip pointed at the display from above.

[@CuriousMarc]

Sounds like a good idea to me!

[@BobHannent]

I kind of want to see Marco Reps making his own ramp based multimeter now!

[@38911bytefree]

Thanks for another brilliant elevator music learning !!!

[@beamsio]

You should also talk about the isolation on the digital communication between the ADC and CPU, it's a pretty neat circuit using magnetic coupling.

[@inothome]

Are three pronged soldering irons really grounded? I live in a country (Vietnam) with no grounds, so everything is two prong and not polarized either. Electrical distribution here is a TT system, no combined or separate neutral and ground / earth. Next time I am back in the US I'll have to Ohm out my soldering iron there. For some reason, never gave it much though, but definitely something to be aware of and I should have known. Unless of course I have a two pronged, double insulated soldering iron there, it's a Weller, not cheap crap.

[@CuriousMarc]

It’s easy to find out. Just measure with an ohm meter from the tip to ground. My Weller is sure grounded.

[@inothome]

@@CuriousMarc For sure, that's exactly what I'll do next time I am back with that iron.

[@bartoszkazmierczak7249]

You may want to take a look at the mains voltage switch. In my unit there were 2 Rifa capacitors hiding inside the heatshrink tube covering the switch. Given the age of those meters it's probably a good idea to replace them because their failure mode is quite spectacular... Mine were in pretty bad shape.

[@graemedavidson499]

5.5 digit - oh, it’s the display and not the price!

[@douro20]

I almost got a Fluke 3800A for free once...one of the first 5-1/2 digit DMMs from the mid-1960s, complete with Nixie tubes. I only got the boards since the guy tore it apart before I got to it.

[@CuriousMarc]

Aargh!

[@tehlaser]

9:02 egad, that’s a lot of 📈📉📉📉📈📉📉📉📉📉📉📈📈📉📈📉📈for one measurement

[@emdxemdx]

@5:33 those look a lot like Apollo switches! 😍🤩

[@moo3993]

I'm not sure if KZbin removed my comment or not but I figured I would try posting again without a link. Marc! This guy by the username RetroFreak84 purchased an original live broadcast recording of the Apollo lunar landing, I'm curious if your camera is the one in the live demonstration. Either way, amazing to watch this in such great quality!!! I've never seen it all the way through. Should be his most recent video, it says 6 days ago for the upload date.

[@CuriousMarc]

This link: kzbin.info/www/bejne/fWHFmYyQbrufoMk . It’s the slow scan camera from our Apollo comms episode 21: kzbin.info/www/bejne/j3PTnZiOgrmosJo . That would indeed be the camera hooked to our system - if we had it. This video of the landing is thrice removed from the original. The original was slow scan. Then it was converted to NTSC by an analog projection system. Then it was broadcast. Then it was recorded on a video recorder. But it’s a clean representation of what people over the world would have seen live on their TV set.

[@hymermobiler]

Another fascinating video thanks for posting!

[@bengelman2600]

The battery vivisection was pretty cool.

[@NielsHeusinkveld]

If I'm ever in an elevator where music is playing, I expect CuriousMarc to start talking.

[@SarahKchannel]

One of the nice things living in the US, you can get used old equipment like this without having to shit them around the world> Where I live in the middle east, just shipping cost will cost as much as a lower cost new one, let alone the repair cost. That is one of the few things I really miss to live in the 'other' world.

[@mrl22222]

I feel you saying you have a "soft spot" for HP instruments may understate things just a bit.. :)

[@danmenes3143]

The converter design is halfway between a ramp converter and a sigma-delta converter. I find it interesting how closely related those designs are.

[@pauldorman]

I have two 3478A's. Lovely things, though I need to get one of them calibrated. I also have a 3456A, which is another venerable instrument. I'd love to get some genuine front binding posts for the 3456A as the original plastic has degraded to the point where they are falling apart, but I've had little luck finding some. Any viewer (or CuriousMarc!) tips on where I might find some would be greatly appreciated!

[@CuriousMarc]

Ah, the original binding posts. I would like to know where to find them too!

[@pauldorman]

@@CuriousMarc that sounds like the kind of problem that people could get behind! I wonder if there would be enough interest to crowdfunding a small run of replicas, for not just the 3456A, but for any HP instruments that use the same design. PCBWay include custom injection moulding in their service catalogue, and there's probably a source for the metal hardware.

[@nickgalena1]

Another questions to your imac repair video years ago: My imac late 2015 has the purple edges all around the black frame (well known problem without solution) . So on IFIXIT you can find "around the edge is just where you put the double side tape to fix it to the case, exactly where the inner side of the double tape makes a boundary, there are some plastic bezels or framing stuff. this plastic actually is not only a guide to mount the LCD panel in the right position, is also a kind of seal that blocks the external source of light." - So does it help to glue this small gap between the plastic bezels or framing stuff to repair the pink edges around the screen ? I think that would be logical.

[@bobert4522]

I was totally expecting that lithium battery to start bubbling out when you soldered to it. Especially since it’s charged. I haven’t been as lucky 🙃

[@Ojref1]

I never forgave HP for selling off its metrology division. I think it was a short-sighted mistake.

[@johnprouty6583]

@Ojref1 do you mean when they spun off the T&M and Life Sciences businesses?

[@rossr6616]

was that under carly fiorina?

[@johnprouty6583]

@@rossr6616 It was before, Lou Platt was still CEO of HP the first yearish of Agilent as I remember it. I do remember a conversation with Lou Platt about Carly before she started (my wife and I were part of a group that were the winning bidders for a dinner prepared by Lou and Joan at their house that benefited United Way) and at the time everyone seemed very optimistic about her coming in. History left us with the reality. But the CEOs after Lou are a whole other story of how destroying, not adapting, a deep culture can gut a company. Just my opinion, I worked for HP for 18 years and Agilent and then Keysight for the remainder.

[@antronargaiv3283]

Whenever I replace a battery, I write the month and year on the new battery, I also put a label with the same information on the outside of the equipment.

[@darrenerickson1288]

Did you just diss Keysight? 😮😵 All you did was tell the truth, vintage HP kicks anything else’s tail, yes. But I hear George Takei going, “Oh, My!” 😂. I so want the desktop BK analog VOM I grew up with in my Dad’s shop in the 70s/80s.

[@johnwilliamson467]

Have to agree as I have 4 3455a all still well in Cal .

[@TheDefpom]

A floating input like that looks like capacitive coupling, I have seen that before, check the front rear switching.

[@Krivulda]

Excuse my offtopic but I don't know how else to contact Eric - I wanted to ask if he is going to finish the MCA SnarkBarker with the CMS addon or if it is a completed project. It's a really awesome project with exceptionally beautiful documentation (HP-level neatness and cleanliness) and I love the CMS sound so I would love to have it on the card too. Sadly don't have the brains to make it work though.

[@CuriousMarc]

Got it. Let me ask him to answer.

[@TubeTimeUS]

it's basically done. i never quite got the CMS chips working on the micro channel card, and i moved on to other projects.

[@Krivulda]

@@TubeTimeUS Aww, that is the answer I didn't want to hear but totally understand. Anyway, if you ever decide to take a look at it again, I can supply you with equations for the GAL chip for the original SB 2.0 if needed. My friend recreated the source code and even fixed a couple bugs in the process. I am sure I can persuade him to give you a copy of the code. :)

[@wtmayhew]

I’ve seen a white filmy substance form on gold contacts in several instruments. Tektronix 2445 oscilloscopes and similar 2400 series instruments have input attenuators with little gold plated moving contacts which can get that film on them. Tektronix warns not to disassemble the attenuators in the service book, but it really isn’t difficult, and cleaning will make an instrument is impossibly noisy traces useable again. … Now if there were a simple replacement for a defective fan motor in 2400 series oscilloscopes.

[@jurjenbos228]

I guess as a result of this video, Wikipedia now has a nice explanation of Multislope on its "Integrating ADC" page.

[@AlpineTheHusky]

Man I want one of those :c. All I ever find is either insanely damaged cheapish stuff or WAY too expensive semi broken stuff

[@nurab-sal1276]

When you do 4-wire measurements with the sense bananas on the outside of the force bananas, you will measure of course the contact resistance of the banana jacks. I guess that's why it's first 33 mOhm, and later it drops to 20 and even 17 mOhm, because the jacks are getting "scratched in".

[@BarryRowlingsonBaz]

Is there a reason you wouldn't solder in a socket for the battery to make it easier for the next person?

[@leisergeist]

Funny, I got a free Tektronix DMM4050 (absolute score, practically new!) with the same sort of rear/front input switch, and had the same problem with it… totally different style of switch, but some deoxit fixed it right up I guess not everything changed between then and the 2008ish mine was made lol

[@VoidElectronics]

Gotta love the metric warning. 🤣🤣

[@mx0r]

Maybe it was answered somewhere already (tho I quickly scrolled thru the comments and haven't found it). Why have you soldered the battery back and not added some holder for it, so it can be easily replaced later? Or there is no standardised holder for it? I understand, it may be a bit risky, as it could potentially wiggle out of the holder, but then, you can stick it with kapton or something. And next time, nobody would need to do soldering.

[@CuriousMarc]

Hey, you do it in **your** instrument. It's your calibration to lose ;-)

[@mx0r]

@@CuriousMarc I supposed that was the reason. 😅

[@mfx1]

The shot of the advert for the 3468A clearly shows the HP-IB logo yet you say it didn't have it?

[@georgealdredge2806]

Look closely, it says “Designed for HP-IB Systems”. The 3468 only had the HP-IL interface, but you could buy an interface to talk to HP-IB. I had one of these twenty years ago a former job and was tasked with making it talk to other equipment that was IB. A guy in another department understood my situation and pitched an HP 82169 interface on my desk and said “Good luck!”. Never was able to make it work as advertised. 😂

[@CuriousMarc]

Only the 3478 has HP-IB. The 3468 has HP-IL. [Edit] But you are right, it has the deisgned for HP-IB logo next to the handle! Typo I suppose? HP was usually very careful with their claims. Unless you use an external converter as you say, but I don’t think that’s what the logo meant.

[@CuriousMarc]

Confirming it’s just a typo. It’s corrected in the HP 1984 catalog, replaced with the HP-IL logo. Good eye, though…

[@robinwells8879]

To build a technical giant like HP you need multiple PHDs. To destroy it … all you need is one MBA!😂

[@CuriousMarc]

Sadly it's not very far from the truth.

[@chargehanger]

Good old Moldymeddar :)

[@bayareapianist]

Hi. I have a 3478a but I accidentally erased the calibration. When I turn it on, it flashes calibration. Does anyone knows how to calibrate it or send the link for calibration? Thanks

[@CuriousMarc]

Procedure is in the service manual.

[@tbp-channel8870]

Best stuff learned today.. the Yankee Pesos.. (roflroflrofl).. Mark, you made my day again!

[@buffler1]

what to use to replace the mercury standard battery

[@thomasbjarnelof2143]

I'm not a big fan of soldering on battery poles. It might overheat the separator or the safety valv