Watch out for those old relay logic boards in pre-1980s traction units

I got called to a 1978 Otis traction job in a downtown office building for a car that wouldn't run. The call history showed intermittent floor leveling issues. I spent a whole day checking the obvious stuff: motor generator set, selector, door locks. Everything tested fine. The problem was a single, tiny interlock relay buried deep in the back of the machine room control cabinet. Its contacts were so worn they'd make a connection maybe 8 out of 10 times. It took me three full days of tracing wires with the schematic just to isolate that one failing component because the symptoms kept changing. The building manager was getting really upset about having one elevator down that long. Has anyone else had a simple relay cause days of headache on an older system?

3 comments

3 Comments

stellaperry13d ago

Those worn relay contacts are the worst kind of intermittent fault.

robins8312d ago

Ever find the new module?

jade51713d ago

That was a 1978 unit, so it would have had solid state relays already. Otis started using the Miconic system with those around 1975. The headache is still real, but the failing part was probably a sealed plug-in module, not an old-school open relay with visible contacts. Those modules fail in the same sneaky way.