That trick with the 12-gauge jumper wire on the door lock circuit backfired on me yesterday.

I tried it on a 90s Dover in a Cincinnati office building and it tripped the machine room breaker, which taught me that old solid-state controllers really don't like that kind of shortcut, so what's the proper way to safely bypass for testing on those older units?

3 comments

3 Comments

the_wendy1mo ago

Use a test cord with a fuse in line.

rubyg511mo ago

Yeah, a fused test cord is the only way. Fried a board on a mid-80s Montgomery last year doing the same dumb thing. That quick zap can cook the driver chips. Now I keep a 1-amp fuse in my kit just for that.

lindahunt23d ago

Exactly, that fuse is key. I learned the hard way too, on an old Westinghouse. Popped a driver chip that took two weeks to find. My test cord is just a length of wire with an inline fuse holder from an auto parts store, cost me maybe five bucks. I use a 500mA fuse for the really old boards, they can't handle any surge at all. Saves so much headache and keeps from blowing up parts you can't even buy anymore.