PDP-8/I at the RICM

On 01/20/2012 01:47 PM, Tony Duell wrote: It is. I would think so. If you do the reforming by simply throwing the capacitor on a current-limited supply and not measuring anything (as seems to be the usual method), then a completely defective capacitor may improve a little bit but still be fundamentally broken, and still fail either immediately or shortly after being put into service. The process we used on the PDP-1 project was to start with the power supply set to 0.5V, watch the current until it dropped below specified leakage, ramp to 1.0V, watch the leakage, and so on up to the rated voltage. At each step the current limit of the power supply is set such that the product of the voltage and the current limit were less than the maximum rated power dissipation of the capacitor. (I think there may have been an additional constraint to avoid having unreasonably high current limit settings at low voltages, but I don't recall the details of that.) Due to the current limit, for a capacitor that needs reformation the power supply will be in current limiting, with the voltage slowly ramping to the voltage setting as the reformation proceeds. If the process takes more than a few hours at a voltage step, the capacitor is probably not going to reform, and should be replaced. If you don't do at least some monitoring of the process (not necessarily as thorough as we did), you won't really know whether the reformation is successful. In the PDP-1 restoration, we encountered a few capacitors that had obviously gone bad and did not successfully complete the restoration process. Most of the capacitors completed the restoration process, and at the completion, performed well within the factory specifications. Although there are other wearout mechanisms, we expect that most of the reformed capacitors will enjoy a reasonable remaining service life. Eric