Queertrons

Are electrons that don’t go where they should in a circuit, or worse, go where they shouldn’t.  This week has been spent madly chasing queertrons through the wonderful world of Embraer wiring.  Seems the backlighting on a few overhead switch panels isn’t lighting in our passenger version.  Should be an easy fix, they’re just a handful of little tiny lamps soldered into a conductive material and screwed onto the back of the panel face.  How hard can it be? A couple of hours to relamp the three panels, slap them back into the overhead, and it’s time for a frosty cold adult carbonated malt beverage.   Sure…..

A little background on these panels.  One houses all the switches for the engines and fuel system, the second is for the ice and rain protection system and the third runs the air conditioning and pressurization.  According to the thoroughly accurate translations of the wiring diagram, panel one gets its lighting power from a converter. That power is split off to the A/C panel lights and then to the ice panel.  The connection for the lights is a little bitty coaxial plug on the back of the panel.  It looks just like the RCA plugs you’ll find on the ends of the cables that run from your stereo to the speakers, only smaller.  The power runs through the center pin and then out to the ground through the outer metal circle.  I have one of the sockets the panels plug into that I yarded out of our parts airplane so I can hook it up to a panel and test the lights using a power source on the test bench.  All the lights worked and that’s a double-edged sword here.  It means I don’t have to fight a couple of dozen lamps the size of a rain of rice, but it also means I have to tear into the overhead panel and find my bad wiring.  The back of that panel looks like this:

What I found was the power pin wasn’t contacting its corresponding socket in the overhead.  So I got to go out to the donor plane in -30 weather, find three of these little sockets, pull ’em out and then install them into the good airplane. Those sockets live in that mass of wiring, light assemblies, and gauges.   And they’re small. How small?  Lemme show ya:

 That little brass colored item in the lower right center of the picture is the top of the socket.  The screw with the triangular slots is just about 3/16th’s of an inch across; just about the size of the little button you push on a pen to get the ballpoint to come out.  The wires are 22 gauge; about the same size as the wires running to your iPod earbuds. This particular socket is the easy one on the overhead to access.  I didn’t have to pull this one.  The three I needed were buried amongst warning lights, and wires, thusly:

It’s in there, you just have to look for it.  I managed to take this with a mirror.  Oh, and did I mention there’s not quite enough room between the back of the overhead and the structure of the aircraft to fit a screwdriver?  Welcome to my world…  So using the third thumb on my second left hand while holding a pair of wrenches in both my right hands and a flashlight in my teeth, I removed and replaced all three sockets.  After checking the wiring continuity, I’m pretty certain the lighting’s gonna work.  I couldn’t check….the airplane battery was dead and the power cart was in the shop.

So ya wanna work on airplanes……..

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