TU56/TC11 restoration - Power supply question

Hi Ashley There is an issue with dry tantalum capacitors blowing up. As far as I know, there is nothing that can be done other than hitting them with the power and replacing those that blow. It helps to have a power supply that can handle a momentary shorts or that is fused so it doesn't damage the supply. Wet electrolytics have a problem in that they tend to degrade over time. During normal running, they produce a small amount of gas that is intended to diffuse through the seal. This is a normal part of maintaining the capacitor. The problem is that when you turn one on that has been sitting for a few years, it can do one of two things. One is that it will reform the capacitor but out gas fast enough to burst the seal. This will cause total failure after a short period of time because of evaporated electrolyte. The next is that it will over heat and short. It will usually burst the seal as well. Not much to do here other than replace. One can reform old electrolytics that are still sealed by bringing the voltage up slowly. Here is where many have different opinions. Some say to use a variac and bring the voltage up slowly over many hours to days. I don't like this method but have used it successfully in the past. I prefer connecting the capacitors ( removed from the curcuit ) to a limiting source and allowing the voltage to float up as the capacitor forms. This is a good way to deal with capacitors that are screw mounted. I use a limited source that will allow no more than 5 to 10 ma or 1/4w ( which ever is first depending on voltage for larger capacitors ). Some computer grade capacitors are very leaky when good and may require more than 10 ma but I find few will recover with much more leakage. One should also take care with switching supplies. Many supplies will blow up if the input voltage is below the specified operating range for any length of time. Some switchers will do OK if there is no load and the input is low while some will go crazy with no load. For switchers you really have to form the capacitors by disconnecting and not using a variac. Dwight