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I can across a Grand Rapids HX EFIS on VansAirForce which had an inoperative intermittent screen. Of course when I received it and plugged it into my bench power supply, it worked flawlessly. Very occasionally it would get the screen jitters. I would let it sit for a week and then try it. Well today it failed pretty spectacularly.  I had the case already off of the unit so when it did fail, I could poke around with something non-conductive to attempt to see where the issue was by vibrating cables and seeing if it changed the behavior of the screen. Winner winner chicken dinner, it's the obvious cable here - super long ribbon cable which is completely unsupported. It's ripe for vibrations causing issues.  I released the holding mechanism (pushing black tabs on the side of the connector away from the edge of the PCB and pulled out the cable. I cleaned the contacts with 92% alcohol for good measure.  This cable is ridiculously long. So dumb to leave it unsupported.  Here is the connector. The black portion pushes away from the white portion to release the cable.  It was a little challenging pulling the two black tabs on either side shut when I put the cable back into the connector. Luckily I had the perfect tool - a slightly bent pick tool from a cheap Harbor Freight kit.  The bend end is key to this working as well as it did to grab onto those black tabs to pull shut.  Yup, right here. You need to have some other tool on the other side to pull it closed too, because the connector tends to rock back and forth, leaving it not fully set.  Boom! Fired it up and it worked! No amount of disturbing the wire caused the screen to get the jitters. I wasn't going to leave this as is, because it will just happen again. There needs to be some way to secure the ribbon cable better.  This was not an obvious fix - I starred at this for a solid hour to come up with a solution. I decided I could pull the ribbon cable closer to the main board (away from the display). However, there was some solder joints I on the PCB I didn't want the cable to run against. So I added some of the soft-sided Velcro to the cable to make sure any abrasion would not happen to the delicate ribbon cable.  I was going to use zip-ties to secure the cable. I thought a piece of Ethernet CAT6 sheathing with Velcro attached would offer a proper buffer.  Because I am paranoid about vibration issues, I slightly melted the ends of the CAT6 sheathing to make sure no sharp edges existed. The idea here is the zip-tie will go through this sheathing and push pressure against the ribbon cable wire bundle.  This is the route I took- it required two zip ties because I did not have a single one long enough.  See that cable all nicely compressed! This is the rest of the routing. It's the best I could come up with to secure this ribbon cable. I am not wild and crazy about it, but it's the best I could do and I think will prevent this from happening again. Not a bad $100 grab!  Before I buttoned back up the HX screen I wanted to do one last test - the cold weather test. No better place than putting the EFIS in the freezer for 12 hours. I made sure it wasn't lonely and put some cheese curds next to it.  The HX was certainly a little slow to render graphics on the screen, but it started right up and worked as expected. I didn't run it very long as frost was forming on it and turning to water relatively rapidly. I will mark this EFIS as fixed! 
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Last Modified: October 5, 2024 |