Tektronix SC502 Scope Repair - High-voltage Section

This video describes two repairs of the HV section of an SC502 oscilloscope plug-in. The first and principal subject is replacement of two tantalum filter caps which can fail and cause no visible trace. The second problem is failure of caps in the DC restorer circuit which can cause intensity control and unblanking problems. Both repairs require removal and re-installation of the A5 HV auxiliary board, which is a difficult process.

[@GrandsonofKong]

Have to agree that when assembled those cap leads were full length and easy to "thread" into the board and then trimmed once soldered. Good tip about 2x the farard value for replacing tantalum with electrolytic.

[@silasmarner7586]

That's a new one on me, and I wonder (but doubt it's true ) if it affects the effective bandpass of the input filter made up by the inductor and both caps....

[@cambridgemart2075]

The old style wet tantalum capacitors usually have a sulphuric acid electrolyte, make sure to neutralise any leakage with a water and baking soda paste.

[@t1d100]

Suggestion for cap alignment??? Maybe make a jig from a piece of very thin cardboard... Place the thin board on top of the freed PCB and mark the pin hole placements. Cut slots (a single cut with the scissors, with no extra width) from the side of the board inward to reach the pin holes. Slide the jig onto the cap pins. Drop the PCB onto the cap pins. Solder in place. Remove the jig, by sliding it off of the cap pins. I hope that was clear and that it helps someone..

[@ElectricEvan]

I might have thrown a little bit of RTV748 electrical grade silicone to hold the capacitor in place. Those leads are a bit long and vibration could be an issue.

[@johnglass]

If those caps are not specially selected why not make the job much easier by just replacing them, rather than dealing with the short leads?