Classic Electronics Repair: Reforming a high voltage electrolytic capacitor: Video 2. скачать в хорошем качестве

Classic Electronics Repair: Reforming a high voltage electrolytic capacitor: Video 2.

Welcome back! This is Video Two where we find out how well the re-forming process worked with the test capacitor. The capacitor took about an hour of adjusting voltage, waiting for the current to drop, and adjusting again to get to the point where it reached 500 Volts. At that point, leakage current was still about 2 mA. Over the next hour and a half, it dropped down to about 800 uA (0.8 mA) and I considered the reforming completed. I then shorted the cap, and ran it back up to 500 Volts. It went smooth, and quickly dropped to sub-1 mA leakage. The next step was to check the electrolytic for actual capacitance: It wouldn't register on the Tel-Ohmic, which was a sign that it passed excess AC hum. Checking a new 10 uF/500 VDC cap on the Tel-Ohmic showed the instrument was working: It registered around 12 uF. Operations were then shifted over to the Sencore LC-75 Z Meter: It showed the new cap had around 10.5 uF, and much less than 1 mA leakage. A reference ESR (Equivalent Series Resistance) on the new cap was about 1.5 Ohms, which is good. ESR is essentially AC resistance in series with the cap, and is a great indicator of how well the capacitor can store charge. The old cap was then checked: Capacitance was well short of where it should have been. Leakage did go sub-1 mA, but ESR was well past 20 Ohms. Bottom line: The electrolytic was well under rated value, and had excess resistance, so it's toast. Fortunately, I had a couple of 10 uF/500 Volt caps, they sub well for the dual 8 uF caps. Even better yet, the plug in cap used a standard four pin rectifier type socket, and I happened to have a broken four pin tube, so I was able to salvage the base and stuff the two caps into it. Sometimes re-forming caps works, and sometimes the caps are junk. It was worth a try with this unit. This cap did re-form, but it was ultimately defective. For what it's worth, the second section was excessively leaky: It wouldn't go past 100 volts, and the current was stuck at about 6 mA. It was bad as well. Thanks for watching! -Tom