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Old 727 radar unit drove me nuts for 3 years until a guy in Tulsa showed me one trick
I've been working on an old 727 that's been in and out of the hangar since 2021. The weather radar kept showing ghost returns and nobody could figure it out. We swapped antennas, changed waveguides, even replaced the whole indicator unit one time. About two months ago I was at a trade show in Tulsa and an older tech took me aside. He said check the bonding strap on the radome hinge, it was loose and causing a ground loop. I flew back, tightened it up with a new star washer, and the radar has been crystal clear ever since. Three years of headaches fixed by a five minute fix. Has anyone else run into something stupid simple that took forever to find?
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paulc933mo ago
Man I gotta push back on this one a little. I don't think it was really the bonding strap. I've seen too many people chase ground loops when the real problem was something else they already swapped out without testing properly. You said you replaced the waveguide and the antenna and the indicator, but if that ground loop was really the issue the whole time then all that other work was just wasted money and time. Plus you tightened a strap and suddenly it works, but correlation isn't causation man. Coulda been the star washer just seated something better or you bumped a connector when you were in there. I'm not saying it's impossible, I'm just saying I've seen too many "magic fixes" that turned out to be the tech getting lucky and not actually solving the root cause.
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xena_taylor643mo ago
Well paulc93 I gotta say your skepticism is fair and honestly I've been on the other side of that too many times myself. I swear if I had a nickel for every time I "fixed" something by bumping a connector while looking for something else I'd have a nice little retirement fund by now. The star washer thing is a real head scratcher too because I've seen those things magically fix issues that had nothing to do with grounding at all. But I will say in this particular case I tested it pretty carefully that strap was loose enough to jiggle by hand and the problem went away the moment I tightened it. You're right though correlation isn't causation and I've definitely been the lucky tech more than a few times in my career.
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