Restoration of a Tektronix Oscilloscope
The restoration of a Tektronix oscilloscope has its start when the instrument is dropped on the loading dock. I know it will be the same old story, another bedraggled instrument from eBay. At this point, I already have about $200 CDN invested in the unit, so I am very interested in bringing it back to life. I start with a complete inspection of the outside of the packing, looking for obvious damage, and also to see how well the seller's packing stood up to UPS. I open the box, and do the same inspection inside. Once I have it out of the box, I check it with a Geiger counter to look for any radiation it may have picked up from the arms race, nuclear medicine, or whatever. If everything looks ok, I remove all the panels and blow it out completely with compressed air.
Now another inspection, this time inside the unit. Look at the fan mounts, has the fan flopped around and destroyed other parts? Check for broken glass, especially the crt. Look for obviously burned or destroyed components. Sharp eyes here can save a lot of extra work later. Usually at this point I can't wait to take things apart, so I remove the fan motor for a later rebuild. I remove any stickers from the front panel. Then I power it up
Most restorers of antique electronics will give you all sorts of advice about first power on. I have not had any problems just plugging it in and starting it up. But I do stand well back. Why am I doing this? First, I would like to see how close to operating the unit is. Or is it a parts unit? Secondly, I like to have a baseline so that I know if cleaning it has introduced any new faults. I catalog the operation of the unit, and then it's off to the bathtub
That's right, the bathtub. I know my pictur shows me cleaning a 515A in my kitchen sink, but I quickly graduated to the tub. Lots more room. I first remove the crt, the covers over the HV, and the cardboard covers over the electrolytics. I cover the HV transformer, the LV transformer, and the crt socket. Then I spray the entire unit with cleaner/degreaser. After sittting for a few minutes, I wash the unit out with hot water from the hand shower. Depending on how dirty the scope is, I may do this several times, and also use a variety of brushes for local area cleaning. Once I am satisfied that the unit is as clean as I can get it, I blow the excess water off with compressed air. The it is off to the oven.
Yes, I said the oven. You know, the one in the kitchen. The scope is baked for 24 hours at 130 degrees. This assures that all the moisture is gone. Once it is out of the oven, I am ready to begin the actual restoration stuff
The switches have had all the lubricant washed out of them, so I first use white grease on the ball detent, and then contact cleaner on the contacts. I rinse out the pots with contact cleaner as well. Usually at this point I remove all the knobs for cleaning, and clean up the front panel.
Next job is to run all the tubes through the tube tester. I replace any which are below normal My record was a scope with 15 dead tubes. Once the tubes are tested, I replace the crt (serviced separately) and once again power the unit up. I am looking for any new troubles that the cleaning may have introduced as well as old ones. If things look about the same as before cleaning, I turn my attention to the chassis.
Chassis work in restoration means stripping the rest of the panels off. They are set aside for now. If the chassis or inner panels are bent, I straighten them. While I am working on the electronics, I paint all of the panels and rails, inside and out. Once the scope is ready for calibration, I install the rails and a new handle. Calibration done, I let the scope run for 72 hours, and if it makes it, do another calibration. If it doesn't, I fix the problem and restart the burn-in.
Finally the scope is done. But wait, it always seems like I find one more thing to make better. So the work continues as long as I have time to correct what man has rendered, or something.