Flat flex cable insulation/isolation - Page 1
Forum section: electronics / repair

author: Mephitus
author_rank: Regular Contributor
timestamp: September 02, 2015, 05:01:48 pm
content: I am repairing a 10" tablet that has an issue with the digitizer. Specifically the Acer Iconia A200.I have come to the theory that some minor wear on the flat flex cable that is shorting to the frame. This causes either "ghost touches" or completely missing touches in some segments. I would post pics, but I have to use both hands to unfurl it and would need a 3rd hand for my phone. The attached pic is a replacement digitizer showing the underside of the flex cable in which I theorize is shorting to frame.My idea to fix it is to insulate it with pvc tape or similar. With the extremely tight space tolerance, all the pvc/electrical tape I have is just way too thick to fit properly. How would you recommend I isolate the flex cable from shorting or wearing against anything nearby?

author: TheSteve
author_rank: Unknown
timestamp: September 02, 2015, 05:23:26 pm
content: Your best bet would probably be kapton tape.

author: Mephitus
author_rank: Regular Contributor
timestamp: September 02, 2015, 05:32:48 pm
content: Quote from: TheSteve on September 02, 2015, 05:23:26 pmYes! That should work perfectly, thank you!I always wondered what that stuff was called.

author: Mephitus
author_rank: Regular Contributor
timestamp: September 03, 2015, 02:59:27 pm
content: I was able to repair the flex cable, woot! With some testing and careful observation it seems that there are 2 problems that caused the malfunction. Firstly, the flex cable was assembled slightly out of place. The spacing to fully cover the exposed pads was just over 1mm too short. [See the red box pictured] This exposed area would eventually short to the LCD frame as the adhesive pad connecting the digitizer and the LCD panel was compressed. Secondly, the flex cable had a double-sided tape under the green line area. Which would lift it just enough to cause intermittent loss of connection when moved.The fix was to cover the exposed pad in kapton tape I salvaged from another donor board. [Thanks for the lead TheSteve!] I removed the double-sided tape from under the flex cable and fit a 1mm tall rubber shim over the affected (green) area. This is sandwiched under the primary circuit board framing and now works just fine!A permanent fix will require either complete reseating of the flex cable to the digitizer or replacing it entirely. I dont think I have the tools or experience to do so properly. Anyone have any advice on how I might be able to accomplish this? I do have a junk digitizer I can test with from an old phone (HTC Evo 4G). And worse case scenario, a replacement digitizer assembly would only cost about $31 USD. I was just hoping to get it fully functioning so we can take it on vacation later this month as my 1.5 year old son might need some distraction on the plane.[BTW, the show "Daniel Tigers Neighborhood" from Mr Rogers fame is pretty awesome as far as very young kids shows go.]

author: Stray Electron
author_rank: Super Contributor
timestamp: October 01, 2015, 02:17:22 pm
content: I used to work on HP equipment hat had similar flexible ribbon cables and it took me a couple of tries to learn how to get them out of the PC board mounted connector sockets without damaging them. The connectors are designed to lock the cable in place when you insert it and if you try to simply pull the cable out you'll damage it. I took a thin piece of sheet metal (magnesium just because I had a pile of very thin Mg battery plates) and cut a piece that was just wide enough to fit inside the connector and about 2 inches long. Push that ALL the way into the connector on the same side that the contacts were on and it would release the grip on the cable so that I could get it out safely. Then pull out the piece of metal and you're good to go! I usually just pulled the piece of metal and the cable out together at the same time.The other thing that I learned was given the paper and tin foil construction of the cables that HP used, they would fall apart if you handled it much so you don't want to handle the cables any more than you have to.