Anyone had to micromanage an intermittent low line fault on a Robicon drive

What are you using to look at fault? I believe that is a very small transformer in the back of the controller. Don't remember the name but it always caused a low line fault. Swap it with another car see if you move the problem.

Low line LED on the drive? I've seen that caused by drive board two.

It's an Otis 401 with a Robicon direct drive and it has a control board with fault leds. The low line led comes on once about every sixty or so runs. The processor resets the drive and it takes back off again. I've checked the supply and it is stable. Replaced the drive board and it is still happening.

Replaced the board or swapped with a known good? We've had boards come back from the board shop and still throw a low line.

Replaced with a known good one

Years ago I remember fixing this problem at Monte Fiore Hospital, Bronx NY. by adding a 2.2 micro fard capacitor to the input of the operational amplifier that senses the line volts, but I do not remember the details. NO REPAIR SHOP will realty know where to look unles they have one of those electronic techs with good background in control system that also understand the DRIVE circuit diagrams.

Thanx I'll look into that.