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Back in the spring my GRT EFIS PFD's screen started displaying distorted graphics. I took the screen apart, reseated the connectors and all seemed to be fine again. Until today.  A few minutes after takeoff, the screen seemed to of fixed itself. Wonderful....we all love intermittent issues!  It wasn't meant to last long, the screen slowly faded away.  And eventually was displaying this. Completely incoherent.  Since the last time this happened to me was in the Spring, I thought it may have something to do with temperature. When the temps are cold, the issue seems to occur more frequently. Also, on my last flight before I removed the PFD, the screen was working properly until I pulled 3-4G's, where it started to degrade. That let me know it had to do with something moving inside the EFIS. I made a makeshift harness and plugged everything in at room temperature. Of course it worked as advertised.  Into the kegerator the EFIS goes to be chilled down to 36 degrees.  Hmm, at first once removed from the refrigerator, the EFIS worked as it was supposed to. Not what I was looking for.  Eventually the screen did fade! This is good news!  Once it warmed up a bit it did come back to life.  But then it slightly degraded again. All good news! I can make the screen fail in my home bench.  Knowing the EFIS could exhibit issues in my lab environment, I removed the case and put it back in the cold. I am hoping I can cause another malfunction, and slightly wiggle each connector to the LCD screen to see where the culprit lies.  Out of the cold and powered up, it was garbage city on the LCD.  I touched one LCD cable and BOOM! Screen came to look like normal.  This is the cable I slightly touched. Looks like the main data cable to the LCD.  The cable connector isn't supported at all by anything mechanical. It just sits snug into the connector.  Here is the issue. I removed the zip tie holding the ferrite secure. It sprung up 1/4-3/8". This means in the cable going the the main board, there is some spring tension in the cable. It wants to spring into another orientation.  And this is where the cable was snugged down to. You can really see the spring action in the data cable. I am sure this is causing some stress on the unsupported connector to the main board.  I gently squeezed the cable into a Z shape so that it sat at a much more natural location inducing less stress on the connector,.  I added some zip ties to secure these two cables.  I wasn't quite 100% satisfied with two zip ties as the ferrite still has a little wiggle room. So I added a third zip tie around one of the accelerometers. This thing is SOLID now. I did a few more tests and nothing could cause the display distortions. I have a good feeling this issue has been fully resolved! 
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Last Modified: August 13, 2023 |