IFR 100S Service monitor capacitors

[suenrod]

I have an IFR 1000S service monitor with a fault in the SMPS (duty cycle regulator as IFR called it).
It uses exotic 4 lead low ESR caps. I'm pretty sure it's going to be a bad cap due to the age of the unit.
The SMPS runs at 20khz. How do I figure out how low the ESR should be?

Thanks,
Rod

[SeanB]

Just replace with a regular low ESR modern capacitor, which is almost guaranteed, for a regular panasonic, Nichicon or other reputable manufacturer, to have a lower ESR than the originals. just use a wire jumper to bridge out the input and output leads on the capacitors, and it will work perfectly again.  20kHz 30 years ago was a hard thing for wound electrolytics with a single long tab to do, but modern units in a radial package have absolutely no issue with this, just use ones rated for more than the current drawn on the rails, and if not sure just use a value and voltage slightly higher than the original and in a similar diameter and length case ( smaller than original by up to 30% in any dimension will be fine though) and you will be fine.

I have some really old 100uF 6V capacitors, that are 2inches long and an inch diameter, and I thought that the dimensions had been entered incorrectly, but no they are that, just that they are a regular capacitor from the 1960's, with a rotten compared to modern performance, but back in 1960 they were a good unit.