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Making a new lens from plexiglass is the better solution, however, as both pieces of the original lens are intact, here is an idea... Clean all of the adhesive, from the two original lens pieces. This is probably the tricky part, because you need to discover the solvent that will remove the glue, but not damage the parts. Round up a common home kitchen food vacuum bag sealer. Apply one drop (literally) of fresh adhesive in the middle of the pane. This is probably the second tricky part, because you need to discover the proper glue type. Place the color lens on top. Place the combined pieces into a vacuum bag and run the bag sealing process. As the air is sucked out of the bag, all of the air between the two pieces will be removed, as well, and the glue will spread between the two pieces, perfectly. Let the glue dry, before opening the bag. If you don't have a food vacuum sealer, various DIY solutions can be cobbled together with any vacuum source - shop vac, carpet vac, etc. Just be careful to watch the glue spreading in the bag and stop the vacuum, before the glue gets into it. HTH.

I was given an HP 3439A. I finally have a printed service manual too. Hope to restore it also!

using a differential voltage measurement,at null,you draw no current from the DUT,thus your meter impedance is effectively infinite.

Thank you for posting , great repair!

Nice try on the relay repair attempt, hair is about 0.05 - 0.15 mm diameter (2-6 thou). I got some 0.05 mm manganin wire and its barely visible

This is an excellent example of applied ingenuity, so appreciated by those of us who enjoy collecting and using old test equipment. I have an HP 3439A DVM with the 3443A plugin. I was rooting for you as you were attempting to fix the original relay, but I was just as happy to see the actual solution you came up with. Thanks so much for this post, Gary. You earned a new subscriber to your channel.

HP made so many cool instruments back then. Have a 3400A myself. Was it not possible to clean of the old glue from the display window and glue the two pieces back together?

I've always wondered what a ratiometer was! I've had one for decades without knowing what it was for. Now I have to find out where I've stored it and dig it up! Thanks! I'm very thrilled to have kept it now! By the way, why is it called a ratiometer? I was never able to find any information on ratiometers on the web until now.

An interesting project, always nice to see old gear brought back to life! Can you tell me what type of blade you used to cut the plexiglass? (I'm guessing plywood) I ask because I am currently restoring two bench multimeters that use panaplex displays and one has suffered the exact same delamination. Regards, David

I can’t quite see the full serial number but it looked like it started with 10xx, which makes it 1970,

"Nice and shiny" as Paul Carlson says, the filter replacement was bang on! Looks lovely now.

I tried this earlier in the week and all I heard coming out of the guitar amp was a bunch of clicks and pops. It had the correct rhythm but there wasn’t any pitch to the clicks. Any ideas what it could be?

Oh wow those huge battery banks to power it, awesome! These kind of instruments are fun, dialing in the just the right amount makes for a nice feeling.

Ciekawy przyrząd :) To kalibrator DCV ? Ciekawa budowa. 11:40 to czarne dwa pakiety to co to jest ? Pozdrawiam

Nice! I wonder if it could be modded to make a calibrator by adding an output terminal for the reference voltage source, but that'd probably throw it out of adjustment.

Thank you Gary for another excellent video. :) Maybe you'll also be able to review the HP 740B DC Standard/Differential Voltmeter? It's very similar to the HP 3420B DC Differential Voltmeter but has a nixie display. Have not been able to find the correct test leads for my HP 740B so may have to improvise a solution. Kind regards.

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Hi Gary was wondering if ud be able to help I changed both the capacitors.. still no screen and checking the voltages I not seeing -15 at all. So again I discounnected that board and was still showing low voltage on -15 rail. Would u hv any pointers?

Great explanation !

The amplifier gain is theoretically 3 to maintain oscillation but it needs to be greater or smaller than this if the two RC networks do not track. The negative feedback must cover the worst mismatch or the circuit will give a distorted output or fail to oscillate as the frequency is varied. Typical tandem potentiometers are not matched over the whole of their range.

Nice demo and explanation.

Isn't it possible to open the upper PCB of the module while it's plugged into the mainframe?

Thank you for another interesting video. Part 4 may seem unfortunate for you, but we will enjoy it. The PCBs from that epoch are very sensitive and easily damaged by normal soldering temperatures. I keep a supply of small brass hollow rivets on hand for that reason as the through-hole plating sometimes comes out as well. Regards, David

£90 is a bargain!!😂 Great video once again!!

Nice and clever heatshrink hack :) I love your thoughtful approach to repairing electronics. It reduces waste as well.

Well after turning on my HP3314A after a few months of non use I noticed my screen was blank too. Following your video I had an issue also with the -15 volt rail. It too is the same capacitor problem… thanks Gary for these really useful instructive repair vids much appreaciated.

peace be upon you sir and zamzam water

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I am sure that you have it repaired, by now. But, for fun, my guess is a cap associated with the chopper.

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@21:00 you should probably recap the whole unit, even if they are still ok now, they may not be ok in a months time, at least if you recap it you know it will be good for at least another 10 years, probably longer.

@10:50 I’ve done videos and made a replacement PCB for the 3400A to replace the chopper board, the board can be found on PCBway

18:17 And that is how you can open and service the module while it's mounted in the instrument? 20:48 Sure this is leaking from the electrolytic, or can it just be that someone sprayed deoxit on the pot just over it?

Interesting chopper block. Die-cast aluminum, spare no expense!

The Nixie driver modules are interesting in themselves, they use four pairs of neon lamps driven by discrete transistor flip flops. Each pair corresponds to A, B, C and D lines in BCD code; one lamp is straight signal and the other one is inverted. They illuminate photoresistors on a ceramic plate, connected in a branched circuit decoding BCD into one-of-10 driving the cathodes. The whole board is a discrete transistor counter with carry-out, so they're daisy chained.

Hi Gary wonder if you able to give me a hint just turned on my hp3314 after not using it for a few months and notice im not getting any display anymore.

Watching through the video, I can see where I misspoke. I said that the most significant digit is either a 1 or a zero, with a plus or minus. Not true; the leftmost Nixie is only plus or minus. A zero is implied, and a “1” in the most significant digit is actually indicated by the “over range” annunciator on the right side of the display window. Sorry about this mistake.

Ładny miernik i magia lamp. Pozdrawiam

I love older HP test equipment, their engineers did amazing things with the available technology. Looking forward to part 2! Try plastic razor blades, combined with holders they make the perfect tool for removing the sticky stuff even on front panels. Little risk of damaging any surface. Regards, David

Built at a time when America was at it's Best! Just Beautiful .....

Ładny miernik. Czy PCB jest złocone ? Pozdrawiam

@12:00 you can probably get some 680uF, worst case you could get 2x 330uF

@8:20 most of those are wet tantalum caps not aluminium electrolytic caps, watch out for that.

Suggestion first: I found pointed q-tips made for eye make up which use bamboo sticks. Still fibrous, but they are much better than regular qtips. I got my 339A early this summer. It languished in a barn! but as you said the sealed internals stayed good. Switch faces, so sad. I have been comparing 339A measurements to my HP334A and have not felt need to check 339A, but I will now compare my measurements to what you get. Such fine instruments with beautiful insides. I enjoy manipulating the 334a controls to get a measurement. The 339A's machine prompted adjustments to get a measurement is truly amazing. Analog elegance. I've seen a couple nice demonstrations of this unit on youtube, but your demonstration and explanation are the best. I'm looking forward to your videos.

06:50 - HIFI-fools around the world felt a disturbance in the force :-)

Thank you for your fantastic videos, they are made in a very calm & sympathetic way unlike other U Tubers. I look forward to more! My career started in instrumentation and although I never worked for HP I had a very close relationship with the company.