Attic Finds & Restoration: HP 427A, HP 3300A, Tektronix 561A - Page 1
Forum section: electronics / testgear

author: Wessneroo
author_rank: Newbie
timestamp: July 24, 2014, 04:16:24 pm
content: Was recommended by a good friend and member here to join and share/seek advice on this project. I'm an ME student with only some experience in electronics, so this should be educational. That being said, if I say anything wrong please don't hesitate to correct me. Hopefully in the end I have a decent arsenal of retro test equipment. Robrenz's work has been an inspiration, but no way I will even get close to his level of perfection. The goal is to keep this project low-budget and to use the detailing products and equipment I have on hand, with the exception of any new components that are needed.I found the equipment in a relative's attic. It belonged to a family member who bought it used for their electronics classes in the 70's. Since then it has sat in the dusty attic for 30+ years. I first found the 427A, but in a later visit I uncovered all the manuals and knew there was more good stuff hiding...Regrettably I have misplaced the "first find" dusty photo of the 427A, so the "before" is after gently dusting the device off with a rag.HP 427A:BeforeAfterComing soon...HP 3300A:BeforeAfterComing soon...Tektronix 561A:BeforeAfterComing soon...

author: Prime73
author_rank: Regular Contributor
timestamp: July 24, 2014, 04:34:05 pm
content: awesome projects.what happened to all the after pics?

author: Wessneroo
author_rank: Newbie
timestamp: July 24, 2014, 04:46:37 pm
content: Quote from: Prime73 on July 24, 2014, 04:34:05 pmOops, there aren't any yet - it's a work in progress. I meant to just put some placeholders so I would remember to add the "after" pics when I am done.

author: Prime73
author_rank: Regular Contributor
timestamp: July 24, 2014, 05:46:32 pm
content: I wonder is there an easy diy technique to restore/redo silk screen on old front panels? i.e. how to restore it to a "like new" state? I have a few old pieces of equipment and plan to start restoring these as well.

author: Wessneroo
author_rank: Newbie
timestamp: July 24, 2014, 05:47:26 pm
content: Here are some details of the first 11 hours of work... It is mostly done, but I am waiting for new banana posts in the mail (these are beyond repair) and am practicing a technique of refilling the stamped text and markings in the front panel.Disassembly. What a joy to take apart, I really like the modular chassis design. It's nice that the panels aren't ventilated or louvered, as I'm sure the boards would not be this clean if they were exposed to the dirt the outside of the case saw. Nothing looked obviously wrong with any of the connections, so I simply lightly cleaned things up. I didn't do any testing prior to disassembly. Which is nice in a sense... if it doesn't work when I reassemble, the blame isn't necessarily on me!Removed the gauge face which was badly faded and peeling. Did my best to flatten the peel and did a B/W copy onto cardstock. Would have much preferred to either do a 1-bit mode copy or scan and clean up in Photoshop. Unfortunately, I don't have access to a scanner and the copier doesn't have such an option. Since I'm working with what I have I accepted it and moved on. It doesn't look perfect, but it's a reminder of how things used to be.Peeled off the broken paper and lightly scuffed the surface, then simply overlayed the new copy onto the old with spray adhesive. I was confident that the edges of the plate wouldn't be visible once the housing was reassembled, so I quickly zipped around the edges with an X-acto knife. Of course I was wrong (as you will see later) so I will have to clean that up when I go back in to complete the job.A burnishing tool was used to smooth out the air bubbles and to round out the radii of the mirror reveal cut.Carefully reinstalled in the housing and resealed with the factory calibration sticker.On the switch plate and top rail, I used Meguiar's PlastX on a light cut buffing wheel in a cordless drill at high speed. Here is a comparison shot of the left (polished) and right (unpolished).I was pretty happy with that result so I cleaned off the polish, applied a thin coat of synthetic wax, and buffed with a finishing microfiber.The side panels, knobs, and foot rails were polished with PlastX, and finished with Mother's Back to Black. They weren't in terrible shape and with my awful lighting, before and after photos looked identical. If you look carefully on the side panels on the before photos you might see some black dots in the vinyl. This was some kind of nasty oil or tar and was removed with Goof Off (contains xylene, toluene, and other petroleum distallate -ene friends). I think robrenz mentioned this too, but if you're not careful, it will eat clean through the vinyl. Several applications of Back to Black were needed to bring life back to the panels.The exposed chassis edges and handle bracket were sanded with a 220? grit sanding block, then polished with Brasso, followed by PlastX, sealed, and buffed. These photos are after the sanding step.Reassembled, and here is where things stand now:Next steps are to install the new input posts once they arrive, fix the cut gauge face edges, and fill in the engraved lettering. I may also try a more aggressive approach on the exposed stainless chassis edges to get a better finish. For now I think it looks pretty good. Now on to testing...

author: robrenz
author_rank: Super Contributor
timestamp: July 24, 2014, 06:06:00 pm
content: looking goodkeep the pictures coming

author: Wessneroo
author_rank: Newbie
timestamp: July 29, 2014, 12:33:31 am
content: Used nail polish to fill in the engraved text on the front panel of the device. After a few seconds of drying, I removed the excess from around the text with a paper towel lightly soaked with non-acetone nail polish remover. It is helpful to wrap the paper towel around something with a flat face that you can wipe parallel to the surface with so that you don't push into the engraving.Pre-wipe downCleaned offLeft (complete) vs. right (incomplete)Inspecting if more than 2 coats is necessary...Looks good as is!Finished product with a new coat of sealant over the whole pieceI am waiting for new binding posts from eBay. They won't match perfectly, but will look much better than what is there now.For those curious, the parts for the OEM HP posts are: RED/MP18 (HP 1510-0008), BLACK/MP16 (HP 1510-0009), BLUE/MP19 (HP 1510-0037). I found them to be extremely difficult and costly to source so I stuck with some inexpensive Chinese parts. Pomona Electronics makes very similar looking pieces for ~$3.70/ea: PN's 3760-2/0/6.Here is the closest looking parts I could find on eBay.

author: Vgkid
author_rank: Super Contributor
timestamp: July 29, 2014, 12:53:03 am
content: Good job so far, keep the pics coming.

author: Richard Head
author_rank: Frequent Contributor
timestamp: July 29, 2014, 05:38:49 am
content: Well done with the restoration. I have a similar HP audio generator (HP-201 I think) that could do with the same treatment. I'm not sure if I have your patience though!A note on the terminal posts. I used them in a product I manufactured a few years ago and had an issue with them. I found that if you don't have a flat section on the mounting hole they tend to rotate very easily. This is because the plastic thread doesn't allow you to tighten the nut very tightly before it strips. I tried adding an extra nut which helped but it still eventually came loose.My suggestion is to select another terminal post that has a bolt going all the way through the panel.Dick

author: Richard Head
author_rank: Frequent Contributor
timestamp: July 29, 2014, 05:41:35 am
content: I now see that your panel does have the flat sections to stop the post rotating. I missed that. I still say use two nuts on each post though, then it should be ok.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 29, 2014, 07:45:47 am
content: Nice!Though when you say 'didn't have access to a scanner', I think you can't have put much effort into hunting one down. Surely someone you know has one? What about a DSLR camera? If you'd taken a hi-res digital copy of the scale, at least you'd have the option of in future cleaning it up and reprinting it to look perfect.Those banana posts you bought aren't going to look as neat as they do in the advertising photo. I've bought some of those in the past too, and the edges are kind of sharp and cheap looking.The photo of the 3300A is a fine lesson in why things should be bagged up securely before putting into storage. I guess he thought he'd be using it again sometime soon. Oh well. At least the attic apparently didn't have possums.

author: saturation
author_rank: Super Contributor
timestamp: July 29, 2014, 12:24:33 pm
content: Wonderful job. Those binding posts look worn but in good shape, I'd just clean them to keep the unit original. Many metal parts from the 1960s are better made than most today.

author: Wessneroo
author_rank: Newbie
timestamp: July 29, 2014, 02:01:58 pm
content: Thanks all for the positive feedback!Quote from: TerraHertz on July 29, 2014, 07:45:47 amFair critique with the scanner. I have one but after 1 hour of firmware/software updates, configuring, otherwise trying to get it to work I gave up. I just wanted to get back to work. This is a side project for me, and is a stress reliever so it's nice to be able to just sit down and get to work. Hence why I am trying to work with what I have. No worries though, behind the scenes I have several other high res copies that I can scan and clean up in Photoshop next time I can borrow a friend's scanner.Bummer about the binding posts.We'll see how they look when they arrive. Maybe I can get away with wet sanding the original posts.Agreed on the 3300a, sad indeed. I too was going to make a PSA about safe storage. A simple plastic bag would have kept it pristine. It is a huge mess, hence why you haven't seen any progress pictures on that device! Of course it had to be stored face up, collecting all the junk on the face. Now just imagine all that dust and dirt inside the Tek scope due to the ventilated top panel...

author: robrenz
author_rank: Super Contributor
timestamp: July 29, 2014, 03:03:34 pm
content: Quote from: Wessneroo on July 29, 2014, 02:01:58 pmUsing 1 bit mode on the scanner gives incredible results. The threshold can be adjusted but it only is going to output black or white. I did no retouching on the 3410A meter face restorationshown here.

author: sean0118
author_rank: Frequent Contributor
timestamp: July 30, 2014, 08:25:56 am
content: I love these restoration posts, very inspirational. I'll need to buy some run down equipment just to restore it now.Any idea how you would restore the front panel lettering if it wasn't engraved?

author: Wessneroo
author_rank: Newbie
timestamp: August 01, 2014, 09:49:03 pm
content: Quote from: sean0118 on July 30, 2014, 08:25:56 amThanks, it's a fun little project for sure. You would have to have the front panel lettering screen printed. I'm no expert on that, but if I had to do it, I would stop by my local independent print shop and chat. In theory it's possible, but your budget is the limit. I wonder if a shop would have any copyright concerns too... I hope I can carefully clean and polish around the lettering on the Tek scope.

author: TerraHertz
author_rank: Super Contributor
timestamp: August 02, 2014, 01:07:36 am
content: Quote from: Wessneroo on August 01, 2014, 09:49:03 pmYou are likely going to have a pleasant surprise there. Tektronix used a technique of printing the artwork on the aluminum at an intermediate stage during the anodizing process. So the dyes are actually embedded in the very hard surface anodizing layer. They can't rub off with anything short of sandpaper that will remove the anodizing too. With solvents like turps, alcohol and spray cleaners they are indestructible.At least, the 7000 series scopes used that, and I have one Type 3B3 timebase module that also does. So unless Tek changed from silkscreened ink to embedded anodized printing between your slightly earlier model and mine, you'll find your lettering is very robust.You can tell by running your fingernail over the lettering. If there's absolutely no detectable raised bump, then it's the embedded type.

author: Wessneroo
author_rank: Newbie
timestamp: August 02, 2014, 01:08:56 am
content: Quote from: TerraHertz on August 02, 2014, 01:07:36 amSweet! Great input, thank you.

author: TerraHertz
author_rank: Super Contributor
timestamp: August 02, 2014, 01:15:03 am
content: Oh, and wait till you pull those Tek modules out and see the construction technique. Have a chair handy, you're going to suddenly want to sit down. I won't spoil the surprise. But it's awesome.

author: robrenz
author_rank: Super Contributor
timestamp: August 02, 2014, 02:47:17 am
content: Quote from: sean0118 on July 30, 2014, 08:25:56 amThe method I used inthis postcould be used to make a new faceplate graphic. Use a scanner to get a exact scale image of the original panel and then touch it up in photoshop. Then print on the sticky photo film shown in the video and apply to the old panel.

author: rexxar
author_rank: Frequent Contributor
timestamp: August 02, 2014, 05:08:36 am
content: I'm really impressed with your restoration of the stamped lettering. It looks stock, great work!