Flex Circuit disassembly? - Page 1
Forum section: electronics / repair

author: algorithm
author_rank: Regular Contributor
timestamp: November 14, 2014, 08:37:06 pm
content: I have a computer from the late 80's, the keyboard flex circuit is the culprit. I was hoping someone could advise the best way to try to repair it. It has broken traces visibly obvious from inspection. Some traces are "dim" and look worn away inside of the laminate. there is 1 trace that had a drop of something spilled on it and it ate through the laminate. I attempted to use a silver based circuit writer by CAIG. It did not repair the tiny hole through the single trace. (that is 2 times I attempted to fix broken traces with it to find out it failed)I was informed by someone years ago that they successfully peeled the bottom and top layer apart. Anybody have any idea how that could be done neatly?The top layer where the buttons make contact has a green clear color, with bridges of some sort? the bottom layer is clear like a license. The traces are silver, Im guessing aluminum?I contacted many companies in China to get some reproduced, but they all wanted gerber files, and I have no idea how to make 1 of those files. The quotes without gerber files were ridiculous.I would buy another computer, but it would not be cheap, and it would be difficult finding the same model. & the keyboard could be problematic with the duplicate computer.Any help or advice is greatly appreciated. Thank you all!EDIT: here are pictures of the circuit in question, I tried my best, but my camera is garbage.

author: Yago
author_rank: Frequent Contributor
timestamp: November 14, 2014, 09:22:10 pm
content: Might help if you said what computer it was from, someone might have parts.A gerber file is generated from PCB design/layout software.Dave has some videos of PCB design ETC, might be start.The software could also have the ability to import graphics format file, eg a bitmap from a digital photo of a membrane layer (would take some photoshop skills too I think).

author: electr_peter
author_rank: Unknown
timestamp: November 14, 2014, 10:23:17 pm
content: In my opinion, the best way to repair/clean complicated keyboards is to replace them. Otherwise it will be a mess.Do you have details/model number of computer and keyboard? Maybe someone still has some stock or old units?

author: algorithm
author_rank: Regular Contributor
timestamp: November 15, 2014, 11:11:33 pm
content: Thank you all. Unfortunately sourcing a replacement film is out of the question... Its from another country, and the model is quite rare. If I go that route I will just have to buy a whole different computer, I really would like to avoid that...I thought of punching holes through the broken traces with a pin to expose the trace? I doubt that would work though... I thought about using a razor to chip the layer off to expose the bad traces, but I worry it would cut through both layers...Someone suggested I use the conductive ink pen I have to connect the contact pads to the other pads, but like I mentioned... There are bridge joints on the top layer that are not exactly like contact pads. No conductive part is exposed there...I hope I can macgyver this one...

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 16, 2014, 07:29:25 am
content: If you can get to the actual traces near the breaks there is a weird trick I have used for flex traces, if the conductive pen won't work.1. Take a toothpick and smear a very thin layer of glue across the break (plain paper glue should work)2. Take a blade and a pencil and scrape a mound of graphite shavings on the break3. Gently mash the shavings on the break with the toothpick4. Blow off excess and scrape away shorts then let it dryIf it doesn't work the first time repeat. This will only work if both sides of the trace are exposed, but should fill in even a small tear in the laminate.Edit: this may work with holes through sandwitched layers but I haven't tried it.

author: dexters_lab
author_rank: Unknown
timestamp: November 17, 2014, 02:56:15 pm
content: i repaired an old Atari keyboard, design fault, the ESC key slowly wears through two of the traces on the membraneused a fiberglass pencil to cut through the mask, then painted conductive paint on... i have also used some bits of fine copper wire (like out of some signal wire) and painted them into the damaged area, this can be useful if the plastic has split

author: TheBay
author_rank: Unknown
timestamp: November 18, 2014, 07:45:11 pm
content: Make and model would really help...I'm guess it's an MSX?Something like this?

author: algorithm
author_rank: Regular Contributor
timestamp: November 21, 2014, 12:47:02 am
content: Actually TheBay, that is nearly the exact model. Yes it is an MSX.I actually ordered the same model in your picture for a replacement film, and it got "lost" during shipment... By the time I got my refund, the currency exchange had changed, and I lost money... It was not a fun experience.Again though, buying a used film might entail the same problem... something I recently considered nearly a year after losing that through the mail, is the chance the film could be slightly different also...Thank you dexters_lab, that is the route Im going for I guess... What side should I cut through? clear side, or green side? Someone implied the green layer is conductive.both of your names are great. especially dexters_lab, brings back memories from when I was younger. (laughs)

author: Macbeth
author_rank: Super Contributor
timestamp: November 21, 2014, 01:34:34 am
content: Ugh, this reminds me of my old Psion 5. Yes, the flip keyboard and display was a thing of beauty, however the contrast on the display was utterly useless. Thankfully I paid extra and got the backlit one.All of the signals going to that display and mainboard went through a shitty flat-flex that was clearly not up to the job - being rolled back and forth constantly.Funnily enough, something like 50% of Psion 5's displays failed just after the 12 month warranty and those cunts at Psion refused to admit it was a manufacturing defect and fix the problem.My brother got a 3mx which didn't have the backlight - it didn't need it as the contrast actually was really quite good. Not like all the false advertising of the original Psion 5 and it's shitty display that somehow looked just like a modern e-Ink in all the adverts back in the day.I managed to solder some ugly wires on to restore the display backlight, but had to treat it gingerly ever since. I've still got it somewhere, complete with all my old contracting timesheets on! I need to dig it out I think. When you could have it in perfect conditions, backlight on, under fluorescent lights in the office, it was actually really very good.

author: algorithm
author_rank: Regular Contributor
timestamp: November 21, 2014, 08:46:11 am
content: Quote from: Macbeth on November 21, 2014, 01:34:34 amI genuinely LOVE that green glow... Recently been wanting to get a green monochromatic monitor just for the glow...& Yeah, I can not say for sure because I bought this computer used, but I would not be surprised if it was a design flaw. Looks like the spacebar smashed the flex circuit 1 too many. If someone babied it, it might be good. Does not help that most of the computers games used spacebar as the main button. I imagine some kid in japan just went wild on it due to his lack of a controller when it was new. Might have exchanged hands over the decades as well.

author: Macbeth
author_rank: Super Contributor
timestamp: November 21, 2014, 10:38:55 am
content: Quote from: algorithm on November 21, 2014, 08:46:11 amYou mean when the little blighter discovered Hentai?