Had a perfect week troubleshooting a Cessna 172 panel swap then everything went sideways

Last month I spent Monday through Wednesday replacing an old avionics stack in a 172 at KAPA. Everything lined up, no pinched wires, all the connectors seated perfect. Got the GTN 750 talking to the autopilot on the first try. Thursday came in thinking I'd breeze through the certification and the GPS antenna cable showed 50 ohms on the meter. Spent 5 hours pulling headliners and chasing a bad BNC connector that someone crimped wrong back in 2018. Has anyone else had a job where the easy part was the hard part and the hard part was easy?

2 comments

2 Comments

spencer_gonzalez15h ago

Five hours for a bad BNC connector from 2018? Sounds like you got off lucky honestly. I've seen guys spend two weeks chasing a gremlin that turned out to be a single strand of wire touching a screw. The meter was telling you the truth, the cable was bad, just took a while to find it. This whole "easy part was hard" thing is just how avionics work. It's not some deep mystery, it's normal troubleshooting. You replaced a whole panel in three days, that's the real story here. Does the plane fly right now?

quinn60649m ago

Honestly, did you check if the BNC connector was crimped onto the right cable type in 2018? I've seen shops use RG58 on a install that called for RG400, the impedance reads fine at the connector but the cable itself drops off over length. Also, that headliner pull might've uncovered a grounding issue that was hiding behind the old radio stack. Sometimes a bad install from years ago masks a bigger problem that only shows up when you replace stuff.