Panel swap on a Friday turned into a two-day mess in Phoenix

I was replacing an old DSC panel at a strip mall in Phoenix last month, customer wanted it done before the weekend rush. Got everything wired and powered up, but the keypad showed a constant zone fault that we couldn't clear. Turns out the previous installer had jumped out a door contact with a resistor that was the wrong value, so the new panel saw it as an open circuit. I wasted four hours chasing a ghost, finally called the supplier and they walked me through the math. Has anyone else dealt with mystery resistors left behind from old installs, or do you just re-terminate every zone from scratch?

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hugo2381mo ago

Wait, did you check if the old panel's EOL resistor even matched what the new panel expects? That's the gotcha I've seen bite people more than wrong values, some panels want 2.2k and others want 10k, and if you just swap panels without checking the wiring diagram you're setting yourself up for a headache. I had a similar deal at a restaurant where the old installer had used a 1k resistor because the door contact was actually two contacts in series, so the math only worked out for the old board. Honestly, I've started carrying a small resistor assortment kit in my truck just for this, it's saved me more than a couple of Friday afternoon callbacks. The real trick is to trace the zone back to the actual device before you trust any resistor you find in the field, because half the time it's not even a proper EOL setup anyway.

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