Found a quick way to check for bad coax connectors on the bench

Was chasing a weird intermittent fault on a nav system for a Cessna 172. The signal would drop out, but only sometimes. I got tired of pulling the whole unit and re-running the cable. So I grabbed a multimeter, set it to the continuity beep, and touched the center pin to the outer shield on the connector end I had off. If it beeped even a little, the connector was junk. Found three bad ones in about ten minutes that way. Saved me a whole afternoon of guesswork. Anyone else have a fast bench check for coax before you put it back in the plane?

4 comments

4 Comments

barbara841mo ago

Yeah, that sounds exactly like the kind of headache that makes a job take three times longer than it should. I've had my share of chasing ghosts in wiring, and that sinking feeling when the problem comes back after you think you fixed it is the worst. Your trick with the multimeter is smart for a fast first pass to rule out the obvious junk. Saves pulling your hair out before you even break out the fancy gear.

umam952mo ago

That continuity check is a bit too simple though (it might miss a high-resistance short). A proper insulation resistance test with a megger is what the manual would call for, honestly.

charlesb892mo ago

I saw a guy at the shop last month burn up a control board because the megger test voltage was too high. The manual might call for it, but you have to check the specs for the electronics first. A low voltage insulation tester is safer for modern gear. That high resistance short is a real problem, but so is frying a $500 part with a 1000V test.

emery8791mo ago

Man, chasing those high-resistance shorts is the worst. You get everything buttoned up, power it on, and it works... for a day. Then the weird fault comes back and you're back to square one. I had one on a motor feed that would only show up when the panel got warm. Felt like a total victory when the megger finally found it.