The key is to never lose sight of the fact that in the end it's an elevator. Over the years I've been doing this I seen guys get hung up on noise related stuff only to find out later that there was a loose wire. Always go back to basic elevator first. Things such as loose controller wires, interlocks and gate switches, door limits and safety circuits. Often you will find ten other potential problems before you find the one that shuts the unit down. If we are looking at noise suppression issues remember that MOVs break down over time and should be replaced. Here again a scope comes in handy when you can monitor low voltage power supplies such as 5 +-12 or 15 volts for noise spikes. Poorly suppressed relays will often leave nice glitches on your power supply rails. If you can find a pattern in the shutdowns you are about halfway there. What about a comp rope or chain that occasionally is bumping a buffer switch in the pit? Does the problem disappear if the car is on door disconnect? Installing a video camera to monitor the status led's for a couple of days is another option. Another thing is to verify things with your own eyes.
