PDP-8/L power supply prints and "reforming" capacitors

electrolytic, surely? OK, as you are probably aware, the dielectric in an electrolytic capacitor is an oxide film on the postive plate. The electrolyte is the negative 'plate'... Sometimes the oxide redisolves into the electrolyte, whereupon the capacitor becomes an effective short-circuit. Reforming is a process to redeposite the oxide, and is perfomed by connecting the capacitor to a DC power supply, with a voltage a bit higher than the working voltage of the cap, with a resistor in series to limit the current. The current flow should decrease fairly quickly -- if it's still drawing significant current after a few hours, then I guess you have to replace the cap. Of course if the capacitor is shorted, there can be 2 problems. One is that a dead short on the output of the transformer/rectifier stage may well damage those components, or at least blow fuses. Also, the capacitor will pass enough current to get hot, and the electrolyte may even boil. At which point the darn thing will explode. Most caps have safety vents just in case this happens, but if not you don't want to be anywhere near it! Even worse, the flying bits of capacitor, or the jet of electrolyte, may damage other bits of the PDP8 However, my experience suggests that shorted electrolytics in computer PSUs are _very_ rare. I've only ever seen one, that was in a Canon CX laser printer. All my PDPs, etc, are running on the original caps still, and I've not reformed them. It's worth testing them by connecting them us as though you were going to reform them (see above) and checking the steady current flow. If there is such a current, you need to reform or replace them. -tony