Locating errors on MasterCard

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17. February 2020 by Peter

I bought some additional MasterCards last autumn and installed them last month. As always when I do something other things stops working in a mysterious way.

This time it was one og my oldest MasterCards situated in the middle of the MIP, so it really way one of my first interface cards and has been working flawless.

But then about a month ago after all my rewiring it stopped working, and I got the typical “Grounding error” where an entire row of switches are lit up. Normally this is due to GND from the switches being short circuited with the GND from the LEDs. But I had not done any rewiring! So this one really puzzled me. Meanwhile no switches on the MIP was working.

GND error where an entire row is lit at the same time. Normally due to short circuit between switch GND and LED GND. But not in this case

I have spend a few weeks trying to locate which group of wires had gone bad even though I have not touched the panels in years. Tried to unplug the GND to the LEDs. The error was still there.

Finally to night I pulled out out all the wires from the mastercard. And there it was! The cause of all my frustrations.

The main chip on the mastercard had come loose!

Notice that chip at the bottom of the Interface card (Just above the table “2”)

When I installed the additional MasterCard in the overhead panel I removed a set of wires going from the annunciator stack on the MIP MasterCard to the overhead. In that process my fat fingers must have pulled the chip as well then taking out the wires.

One gentle push and the chip went back in and voila now it works.

Of course I now have to reconnect all the wires and re-configure them.

Lesson learned: None!
These are just so typical my cockpit building. You fix something and something else comes loose and you can spend an eternity trying to figure out what / where / why.


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About BuildaBoeing

My name is Peter and I live in Denmark.
I am building the cockpit of a Boeing 737 in my basement using my limited skills and inspiration from fellow builders.
I post my progress on this blog and hope it can be an inspiration to others.

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