In a previous post, I had documented the condition of several RIFA Y Safety capacitors, clearly showing the cracked condition of the outer case. This condition is a precursor to the well documented failure of this style of RIFA capacitor. Reportedly, these problems have been solved since Kemet acquired RIFA in 2007. Of course, the equipment which contains these potentially failing capacitors is typically older than 2007.

For example, I recently replaced six (two from each instrument) of these capacitors from the following equipment:

Each and every RIFA Safety Capacitor I removed from this equipment showed cracks in the case.

These capacitors are connected from line to ground and designed to fail “open”. Unfortunately, these RIFA capacitors failed short and could result in smoke and fireworks. Why is this?

Examining the partial schematic shown below (HP 3245A AC Line Input) we can see that the two lines to ground safety capacitors are always connected to power, even when the main power switch (S3) is in the off position. If the safety capacitors fail open as they are designed to, then there is no danger and no fireworks. The capacitors no longer filter line noise, but the instrument will still function. However, if they fail short (as do the RIFA capacitors we are discussing) then full line voltage and current is applied to ground through the capacitor. This results in noise, smoke and fireworks.

Update (November 2023): I have found more of these damaged RIFA safety capacitors in several pieces of HP 70000 equipment I have been restoring including the 70001A and 70004A mainframes:

The HP 70001A Mainframe/Power Supply has 11 of these safety capacitors, and they all had cracked cases to one degree or another. The worst ones also had visible cracks in the electrode material. All were replaced with appropriate modern X1/Y2 safety capacitors. I found more cracked RIFA safety capacitors in another 70001A mainframe and a 70004A mainframe. All were replaced as required.

I feel much better having replaced the suspect RIFA capacitors with modern X1/Y2 safety capacitors.

Thanks for reading.

Equipment Restoration HP 3245A HP3458A RIFA Safety Capacitor Failures Shaun Merrigan