Restoration Date: October 2013
The style was unique and was based on the "Pocket Scope" by Waterman Products who made it for Philco. The Philco S8200 (originally model 7020) was sold for television servicing business in the early to mid 1950's. Picked this up on Ebay and was non-operating. The oscilloscope was previously worked on. Many of the large value capacitors were replaced and was sloppily installed. The person probably gave up because the oscilloscope did not work. As I worked on this, some interesting things "popped" up and are worth discussing about here.
I took a chance and turned it on before I worked on it. Result nothing on the CRT. This could be many things. The vertical and horizontal amplifier circuits were not working (which is relatively rare for basic 1950s oscilloscopes like this. The CRT has a non emitting cathode which I have seen happen in vintage TV's. The high and low voltage power supplies have bad electrolytic filter capacitors and associated circuits dealing with focus, beam and deflection were not functioning. I decided to go for the power supply first.
Finding the schematic was difficult. I knew from others that Waterman Products designed the oscilloscope, but this was built to Philco specifications. This model features a low voltage supply using a 6X4 full wave rectifier tube and a high voltage power supply using a 1V2 TV HV rectifier tube. I found a Waterman S14a oscilloscope on the internet that used this supply design and was wired similar to my S8200.
A. Power Supply Repair/Restore
B. CRT Bad?
If the CRT was bad, nothing can be seen. This is rare because unlike TV, oscilloscopes are used much less so less wear on it, unless the bad power supply cause components to fail, damaging the filament and cathode. I manage to order one for a reasonable price, if the CRT was good, I now have a spare which would be even better!C. Finishing it up
With the correct schematic found out that the wrong value capacitor was used for one of the range steps for the sweep control. The person installed a 0.0025 uf when it should be 0.02 uf. This would change the sweep width across the CRT. The correct value solved the problem. Replaced and reinstalled all the capacitors that were replaced or checked bad before so it will look more professional. All other resistors checked and replace if out of tolerance. Reinstalled the can covering on the power supply electrolytic. Put everything back in and did some cleanup and adjustments.Return to Restoration HOME Page: Restoration HOME