Any Idea how i repair this missing pad ?

[dimlow]

I have an bought on old psion 5mx of ebay that was meant to be working! when i received it, it didn't work. These are notorious for the flex cable breaking between the main PCB and the LCD because of the funky way the screen folds down and the keyboard slides out. The seller refunded me but i thought id repair it. I managed to get a new flex cable. Whilst removing the old flex cable i managed to pull off a pad as you can see in the picture. The flex cable solders direct to these pads. Any thoughts on how to repair it ?

[bilko]

You could use the silver paint that is used to repair rear heated windscreens, available from rswww.com , I believe

[Neilm]

You could try using a very thin piece of used solder wick. Just solder it to the via and let it go up over where the pad was.  Just be very careful when soldering.

Neil

[Alex]

It is a delicate procedure, before you proceed check if there is any other way around this, like a direct cable connection.

Using dry adhesive:



Using epoxy:



In any case you will need a replacement pad that you can make from copper sheet. You will need to connect this to the via on the PCB, you can use silver-loaded epoxy or solder.

Alex

[dimlow]

I have tried using the silver conductive paint before, that has never worked for me. What i think i might do is run a small wire around from the back of the via once i have soldered the new flex cable in place, the tuck it under the flex cable and solder it does that sound ok ?

Those video's make it look so easy to repair a pad but the pad in the first vid was stll attached and in the second there was no electrical connection, i cant see the point of repairing a pad with no electrical path. I have see some of the other BEST video's they always make it look so easy.

[tekfan]

You can get copper self adhesive tape at a crafts store. I've repaired several connector contacts this way.

[Alex]

Objectives are reliable electrical connection, but the question is how reliable do you want the mechanical connection? Is the pad on the flex cable intact? How much space is there for a strain relief technique? Anything will work if you then secure it in place with epoxy, I am worried about your proposal to use a wire raising the adjacent pads too high.

You can cut a small stripe of copper foil. Shape it as a 1cm long rectangular pad. Flip the flex connector to see the contacts and add a tiny tiny amount of solder on the equavalent pad on the connector. Add some flux in paste form to act as a gel which whould help you align the copper stripe. Hold the piece in place with pliers and heat it from the top. Allow to cool. Place on PCB and solder the ends of the flex to keep it in place, plus some more pads further inside. Allow to cool. Cut the copper stripe to length so as to reach the via. Place flux under it and quickly solder it on the via. Allow to cool. Quickly solder the remaining pads on the flex.

See attached. I doubt that the epoxy will cause signal degradation issues. Take a picture for our enjoyment 

EDIT: The pad will not have enough surface area under it for self adhesive copper to be reliably mounted, it is the solder that will hold it in place. You could use that instead of flux paste for alignement, but you will burn the glue under the pad. It should have similar results. If you dont have copper tape, take a piece of thick solid core copper wire and hammer it flat. The use your wire cutters and cut a rectangle stripe.

Alex

[dimlow]

Great description and great way of doing it, but there is a small variation as this flex cable has a fold at the end were its soldered to the board that may make it easier to fix with a jumper wire. I did a picture its not up to your standards Alex, but i hope you get the meaning of what im thinking.

Edit, i dont get the new Flex cable until Monday (post) but will show results when i have done it, Also the flex comes off the board to the left, not the right as you have drawn it, so that also makes it better to fix.

[Alex]

Can't beat serviceability of old handware! I hope the seller doesn't watch this forum.

[Psi]

I hope the seller doesn't watch this forum.

hehe, doesn't really matter, i bet he will spend more time fixing it than what the original seller was selling it for.

[Lawsen]

I have tried this conductive ink pen to repair computer and amplifier with limited success.  Soldering a jumper wires are best for amplifier.  I do not see any room for soldering jumper wires in the Psion palmtop or hand held computer.  Try this conductive ink pen, that it might work. 

http://www.maplin.co.uk/conductive-pen-33837

Lawsen

[dimlow]

hehe, doesn't really matter, i bet he will spend more time fixing it than what the original seller was selling it for.

I will probably enjoy fixing it more than i will using it, I'm constantly on the hunt for faulty items on eBay to repair. This was just a little bonus item to repair. Sometimes the repairs are  not cost effective but still I enjoy the challenge. Only spent about ten minutes on this one so far

[LEECH666]

I once repaired a broken track on a PCB, back when I worked at Thales Naval. The problem was the Track was underneath a an IC.

I used 0.8 mm silver wire and flattened it with a hammer and a vice to form a track segment. I cut it to size and soldered it onto the broken track.
However the PCB was coated with varnish. After I ran some tests on the fixed PCB I repainted it with varnish.
Might work here too. I would give it a try, but it might be more difficult in this case.

Florian

[dimlow]

Well Post man has been and no flexi cable, so wont be fixing it today.

[Psi]

I used 0.8 mm silver wire and flattened it with a hammer and a vice to form a track segment. I cut it to size and soldered it onto the broken track.

Got to love any electronic repair that involves a hammer

[LEECH666]

Haha, indeed. It was some military gear from a German tank (Leopard II), and I fixed the problem this way. I really just used it to flatten the wire into smth that was like a pcb track. Better than conductive silver imo. No force was applied directly to the PCB .

Cheers,
Florian

[dimlow]

Opps, i fixed the Psion, its working well, now but forgot to take photo's, after all i just a jumper wire and didnt fix the via.