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A lovely VTVM. What else would you expect from old HP? It was top notch. Nice job on the needle meter and again, beautiful innards.

That's gonna get you into building synths, haha!

Hi Gary I hv when all other boards are unplugged +15 -15 +5 volts rails showing correct voltages acrross the cap on +24 v rail i hv +31 volts and across the cap on -24v rail -32 volts and the led comes on on the board. However when plugging in the other boards the voltages drop and the led does light also no readout on the front panel the voltages show +15v = 11 v -15v = -1 v +5v = 0.5 v across cap on -24v rail = 0 v and across cap on +25v rail = +30 volts… could you help where i need to check whats causing this please

Nice! I prepare a cup of coffee to see this video...just 2:30?? 😊

Very classic, nice and simple.

I built one of these in electronics class way back in the late 70's, likely around 1977. An absolute blast.

I would have used retrobright on all the button caps as well. My 3325a looked like new when i did mine a few years back.

Yes, those Mostek ROMs are known to fail, not sure why but it's more common than you'd think. Had a bad set in a HP 3456A once myself, for instance.

It may have been easier to cut off the plug end and wire in a replacement. I like the Leviton "Black & White" series, also sold at Home Depot.

A clever (upside down) and elegant (in its simplicity) repair trumps a little bit of your age showing in the solder joints. I have that same age challenge, so I commiserate with you. I do think your solder iron tip may have been a little cold, for the job... Or, maybe the tip you used was small and did not have enough mass to carry the reflow all the way through. This is not fault finding, but is intended to help you find a work-around. When I have marginal heat, I also cheat, by applying copious amounts of flux. It encourages the flow out that little extra bit. You did an amazingly great repair! Kudos!

I have model 3440A that I rescued from the shredder in the recycling facility. And it works perfectly fine...

I can see your crack. Don't take that the wrong way.

Liked! Would also enjoy seeing some of the steps you use for component cleanup, testing, etc. Great video!

beautifull instrument!

usually a hum from a transformer is delamination of the iron core causing them to vibrate witch will cause heat as well and yes your correct it should not be getting that hot. i hope this helps some i restore these HP test units as well

Nice work.

Ładny klasyk i działa ... Pozdrawiam

Excellent! These are very rare HP units to come across.

Necessity is the mother of invention. Well done!

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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