Serious question, why does everyone still trust door lock monitoring contacts?

I spent 8 years on Otis and Thyssen units and always replaced bad door lock contacts without thinking. But last spring on a 20 story office tower in Nashville I had a car that kept dropping out of service at random floors. The contacts tested fine with a meter, voltage was clean, no visible wear. I swapped them anyway because that's the standard move, but it kept happening. After 3 weeks of chasing it, I found the real problem was a cracked solder joint on the controller board that only opened up when the car hit certain speeds and vibrated. That board was flagged for replacement in the PM schedule anyway, and nobody thought to look there first because the contacts are the easy answer. I'm not saying skip basic checks, but I think we lean on those contacts way too hard when the fault code actually points elsewhere. Has anyone else had a phantom shutdown that turned out to be a board issue, not the mechanical side?

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abbyhall19d ago

Does your test meter have a peak hold or min/max setting? I caught a similar ghost once where the contacts showed clean voltage but the meter was averaging out a drop that only lasted a few milliseconds during high speed runs. Took me forever to realize I needed to watch the actual waveform, not just the numbers. That changed how I check every intermittent fault now.