PDP-8/I at the RICM

Rob Doyle wrote: You don't need to understand the failure mechanism of a component to monitor for the failure. You only need to understand the observable behaviour of a failing component. Nevertheless, the failure mechanisms of aluminum electrolytic capacitors are well understood. Three of the most common are: 1) oxide breakdown - when not under bias for an extended period, the oxide breaks down, which reduces the safe working voltage of the capacitor. At lower voltages, the capacitor appears to be more leaky than it should be. This can be fixed by reforming the capacitor. 2) catastrophic breakdown - when the applied voltage exceeds the safe working voltage (which may be reduced from factory spec due to oxide breakdown), the capacitor will short out in a spectacular manner. Non-repairable. 3) electrolyte drying out - this happens if the seals are bad, or if the capacitor is overstressed and ruptures the seals. Non-repairable. Sounds like it had oxide breakdown, which then resulted in catastrophic breakdown.