Rant: Chasing a ghost on an RJ100 flap fault ate my whole Saturday

Spent 9 hours on a CRJ200 flap position indicator that kept dropping out on the ground but never in the air. Pulled the PSEU, checked all the harness grounds, even swapped the proximity sensor on the left outboard. Finally broke down and looked at the wiring diagram again for the fifth time and spotted a note about a resistor pack on the #2 relay. Sure enough, that thing had a cracked solder joint inside the sealed box. Swapping that part took 20 minutes and the fault cleared. I know we all say check the simple stuff first, but when the intermittent only shows up after thermal soak, it's brutal. Anyone else had a relay box or sealed module hide a fault like that? How long did you chase it before pulling out the magnifying glass?

2 comments

2 Comments

grant.sam21d ago

Man, how many of us have pulled our hair out on the CRJ flap system only to find it's some dumb little resistor doing the dirty work? My last one was on the 200, same sort of deal but it was the flap load limiter relay box acting up only after the plane sat in the Florida heat for a few hours. I chased that ghost for two full shifts before I finally got out the schematic and a jeweler's loupe to look at every solder joint in that sealed unit. What finally clued me in was tapping the box with a plastic screwdriver handle while wiggling the harness, it would drop out for a split second. Once I cracked that thing open, sure enough, a hairline crack around one pin on a relay base. I ended up reflowing about six joints and coating the whole board in conformal spray, never saw the fault again. Sometimes you just gotta treat those sealed boxes like they're lying to you, because they absolutely are.

the_max20d ago

Ngl, that tapping trick is solid, but I gotta point out one thing. Conformal spray isn't really meant to fix cracked solder joints, it's more for keeping moisture and dirt out. If that crack was truly hairline, the spray might've sealed it, but it could also just be masking the problem. The real fix would've been replacing that relay base entirely, because reflowed joints on a cracked base can fail again once the heat cycles hit it. I've seen guys do the same thing on the CRJ 700 flap proximity sensors, spray everything down and call it done, then the fault comes back three weeks later. Not saying your fix didn't work, just saying the spray ain't the hero here. The reflow and the new solder are what's holding it together, and even that's dicey on a sealed box with no way to inspect it after you button it up.