Restoring a Tek 453 Scope

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The story begins in  maybe 1980, my brother found a discarded 50Mhz Tek 453 scope in his employer's garbage dumpster and took it home. It worked!  He used it for a few years but eventually bought something faster, giving me the Tektronix as a hand-me-down. 

I used it until about 2003.

Restored, working scope.  Beautiful in a 1960's industrial sort of way.

Fast forward many years: I use smaller, faster Siglent scopes; the Tek has been gathering dust for over 2 decades.  

Wasteful--I should make sure it works, then, get it to someone who will use it, right? 

It works here, but at first? nope

POWERING IT UP

Nothing! No fans, no sound, no smoke, no traces visible on the CRT: completely dead. 

Fortunately the schematic and user manual are online (here and here). The 453 is solid state. Also i read that the 453 was designed using no unobtainium ICs or components. 

So--assuming the CRT can be replaced, if it's dead--no matter the issue, this scope can be repaired. 

EASY FIX??

I removed its cover to check the power supply. Sure enough, the power supply was dead (nothing, anywhere); mains fuse was good. Checking mains coming into the power supply: nothing, but it didn't appear to have a short. 

Could the power cable be bad?

**Not** the original mains plug

I opened up the Nema 5 connector and sure enough the positive mains lead was disconnected, so the scope was not getting mains power. Doh!

Easily fixed--I screwed the mains lead back to its screw terminal inside the connector and fastened everything back together.

After that it powered on. Amusingly: after 20+ years as a giant paperweight, the scope's basics worked. The CRT was tired--I had to turn "intensity" to about 70% or more to see traces,  but both channels, one shot triggering, X-Y mode, and the trigger out BNC worked great. 

3D PRINTING SWITCH CAPS

On to cosmetics. I removed 20 years of dust and dirt on the scope and its front panel with a handi-wipe. Easy.

The front panel switches had all but one switch cap missing. I figured modeling the only remaining switch cap with Fusion 360 then 3D printing a dozen or so replacements was in order.  

I hadn't used my 3D printer in a long time and forgot pretty much all of it.  

That's why I have this blog, a trail of crumbs right? 

Original 3D how-to post for my bench is here. 

I rewatched the Fusion 360 for beginners video here.  

The Voxel printer uses its own slicing software--Flashprint MP.  As far as I can tell, other popular slicers like Cura still don't work with the Voxel IIIP, you have to use Voxel's slicer. I had forgotten that too.

I wanted to make the replacement caps to look as much like the original as possible.....I couldn't find a switch cap I liked on thingiverse. Time to roll my own.

The original switch cap was carefully measured and drawn out:

Fusion 360 bench notes:

• Save your design before you start doing anything to it.
• Fusion 360 saves everything in the Autodesk cloud--you knew that right? I didn't.  If you want to save the file locally you have to export it.  
• make your origin planes visible--otherwise you can't tell up from down, really.
• You create 2D drawings in Fusion 360, using a"sketch"  You right click on a plane and then choose "new sketch".
• Hitting "S" in sketch mode brings up a very useful dialog: start typing center and find the center rectangle tool, for instance. Now you can draw centered around the plane's origin. Much easier than trying to find things via the menu and icons--beside, Autodesk keeps changing the Fusion 360 UI, so videos showing you where things are are often out of date/inaccurate and thus frustratingly difficult to follow.     
• Hitting "Q" allows you to extrude, turning 2D into 3D.  
• I could extrude holes with offsets from a flat sketch, but not from a curved one. In the case of this part, I had to cut a 50 mil x 135 mil rectangle so the cap could be pressed on the switch.  I did this from the bottom plane with 100 mil offset, extruding the cut to about 200 mils above the top curved surface. The same cut couldn't be done from the curved top down, but this bottom-up approach worked.
• You can scale the entire part--useful for fine tuning its fit. Lasso the entire part with your mouse, click on "base" in the nav tool to the left, then click "Modify" along the top.  In the dialog that pops up, 1.15 means 115% larger than what you have now. The same can be done in the Flashprint-MP software for my 3D printer, which turns the stl file into a gx file to send to the 3D printer. I found the scaling freatures in Flashprint-MP easier to use vs. Fusion 360's scaling feature. Why did I need to scale the part? The caps needed about a 105% bigger cutout to snugly fit on the switches in spite of careful measurements done previously. I figured the extra 5 percent was needed due to slop in the printing process--not sure, but pretty easily fixed--I expanded the entire STL 1.05 before printing; after that the caps fit perfectly. This may or may not be needed for your printer setup.
• Don't use inches or mils when creating 3D models--ever. Use millimeters instead. Flashprint-MP slicing software only works in millimeters, and sending it stl's crafted in inches drives it nuts.  Fortunately when exporting the stl file from Fusion 360 I could choose millimeter scale, even through 3D model was created in mils; now Fusion-MP was happy with the source file.

Let's print!

I was afraid the base of the part was too small to stand upright while being printed but the Flashprint software was smart enough to create a flat base around the part. It printed perfectly:

After printing I tried different means of removing this flash. 

What ended up working best was to cut the base off with household scissors, trim further with an xacto knife, and finish up with a 300 grit filing stick. If I spent time carefully cutting and filing the switch cap came out almost perfectly--very hard to tell from the original. 

But...I didn't end up spending too much time filing to perfection--no point as I saw it....Instead, I got the switch caps to where they were good enough. Time to move on!

PAINTING 3D PARTS

This was something I had never done. Would the paint stick?  Would it turn the plastic into goo? Not sure. 

But--I used ABS (or was it PLA?) filment and read online that painting either type of plastic was easy. 

I used Rustoleum "2x Ultra Cover" black and grey primer--I found this recommendation on reddit--two quick coats and the switch caps looked great.  

Pressed the caps on the scope--done.  

if anyone else needs the stl or gx switch cap files, get them here.

NEW HOME FOR AN OLD SCOPE?

For the antique scope--will anyone want it?  Not sure, but it was fun and easy getting the old scope ready for use again.  

Is antique electronics restoration is more fun then AudioDiWhy? Perhaps. In another universe.  

Ah! Finished.

Until then/there, Tek out, captain.