Deja Vu: Another HP 3440A Restoration Part 1

[@TeslaTales59]

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

[@KeritechElectronics]

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

[@garyramsey4275]

@@KeritechElectronics if only it worked as well as it looks.

[@KeritechElectronics]

@@garyramsey4275 it's just a question of time :)

[@t1d100]

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.

[@garyramsey4275]

@@t1d100 seems like a lot of work for an unacceptable result. These pieces were warped and degraded beyond repair.

[@t1d100]

@@garyramsey4275 I did not intend it necessarily for your situation, but to stir up some creative thinking, for people that have a similar situation that might be resolved with some clever thinking. As I said, that, for your situation, the new lens from plexiglass is the better solution. Cheers.

[@TheDefpom]

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

[@garyramsey4275]

@@TheDefpom yes you are correct, it’s 1970.

[@geirendre]

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?

[@garyramsey4275]

@@geirendre I didn’t attempt to do that with this instrument. I have tried this in the past, unsuccessfully. Replacing the window is the best solution.

[@davidv1289]

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

[@garyramsey4275]

@@davidv1289 it was not a plywood blade. A 10” fine tooth (80 teeth I think) carbide blade. Just what was already in my saw. Not sure if that was the right blade to use, but it seemed to work just fine. There was just the tiniest bit of tear out, one tiny little chip, on one corner, which isn’t visible in the end result.

[@garyramsey4275]

I have a zero clearance insert on this saw, but a sacrificial backer board would probably work just as well. And I left the paper on until after I finished the cut.

[@davidv1289]

​@@garyramsey4275 Thank you for the information. I also have a zero clearance throat plate but I still feared chipping and cracking. A backing board sounds like a great idea. I may also try a fine tooth blade in my band saw. And yes, the paper comes off last! I'm working on two Guideline 9577 DVMs (Solartron 7075s in disguise)

[@t1d100]

@@davidv1289 Not only a backer board, but a top board, too, to create a sandwich. Make the boards larger than the lens and secure them through the lens plastic, outside of the rectangle that you desire to keep. Do not over tighten the screws, as the boards will bow up from the plastic and lose their protective clamping advantage. Use counter sinking holes and flat-head screws, to make a smooth gliding surface that won't catch on anything. When cutting, you need to watch your rate of advance... If you go too slowly, the plastic can melt and stick to the blade. (Ask me how I know = grin.) Attention to these additional preparation details will significantly increase your chances of success. I have seen various saw types used. Even a table saw can give good results, with the right type of plastic and blade... Band saw, hand hack saw, jig saw... It's all about the blade tooth and the rate of advancement of the cut. Experiment and make test runs. to find what works best. But, I am sure you already knew these things... Here's wishing you great success and satisfaction... HTH.

[@davidv1289]

@@t1d100 Thank you for the advice! I know what you mean about blade advance and melting- been there, done that. Top board sounds like a good idea, I'll try it. David