Originally posted in November 2020

RIFA Safety Capacitor Failures have been documented by many of us who restore and maintain vintage electronics equipment. One very spectacular failure was caught live here: courtesy Dave Jones of the EEVBLOG. These capacitors were widely used in test equipment manufactured during the late 1980’s through the 1990’s. The consensus is that the capacitors fail because the outer case (presumed to be a type of epoxy) develops cracks which allows moisture to penetrate the body of the capacitor. This leads to internal short circuits which cause the capacitor to fail catastrophically. Because these capacitors are line to ground, they could see line voltage whenever a piece of equipment is plugged in, even when switched off. The crack network can develop to the point where large pieces of the outer case spall off, exposing areas of the electrodes to the atmosphere, adjacent circuitry and creating leak paths.

My own materials lab experience suggests that quick curing epoxy mixtures (with correspondingly high exothermic reaction), while initially dimensionally stable,  can shrink significantly over a period of several years.  Slower curing epoxies that I have used do not exhibit this problem.

While restoring an HP 4192A Impedance Analyzer I found a couple of RIFA Y Class (line to ground) in the power supply circuit. This is a late 1980’s through 1990’s vintage instrument. Close inspection revealed a network of cracks in the outer cases of the capacitors. After replacing them with modern disc ceramic equivalents, I documented the condition of the RIFA capacitors. The outer case had indeed cracked, forming a network of interconnected cracks and exposing the electrodes in some places.

Examples follow:

What we know for certain is that when these capacitors are found in vintage equipment, they must be replaced with appropriate modern safety capacitors. This should be part of the initial inspection/repair process.

Update November 2023

While restoring an HP 70001A Mainframe power supply, I found more examples of badly deteriorated RIFA safety capacitors. These date from approximately 1986:

This HP 70001A had eleven capacitors of this type (a mix of X and Y classes), and all had visible cracks in the outer case.