Key fob contact 'repair'

[jreed]

I recently had intermittent operation on the remote keyless entry fob on our Volvo 850, so I took the keyfob apart and cleaned the contacts, which did not resolve the problem.
I decided to add a copper strip on the push contact. This fix seems to have worked so far. I took some photos along the way while doing this job:


First remove the battery door:

Remove battery door

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Then use a small flat blade screwdriver to pry the back of the case off:

Remove the back of the case

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Then take out the circuit board:

Remove circuit board

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Then peel the plastic contact sheet from the circuit board, exposing the carbon-coated domes that click down under pressure to make contact to the interdigitated electrodes on the circuit board.

Plastic contact circuit with a thin strip of 1 mil (~25 micron) copper sheet

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You need to cut a thin strip of copper sheeting to make new contacts. I used 1 mil copper sheet. Aluminum foil might work too if you don't have copper sheet. I left the copper strips a little long to make positioning easier.

Copper strips cut long and placed across contact domes

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I used cyanoacrylate "Gorilla" glue (like Crazy glue) to hold the copper in place across the contact domes and once it dried I cut off the excess copper strips on either side of the contact areas. A very small amount of glue between the carbon and the back of the copper strip is all you need... don't use too much.

Copper contact strips glued in place

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Then you just reassemble the fob, making sure to get each piece back in the right place (the photos helped remind me what went where).

This fix has been working pretty well for a few weeks now. I'm getting proper operation of the Lock and Unlock buttons every time. I don't know how long the repair will last but so far it seems like a good method. I have read about a "contact repair" product that is supposed to repair the carbon contact material in the switch, but I haven't tried it.

[rspi]

Thanks. I have a remote that clicks good but doesn't work. I'll try this.

[rspi]

I have the square remotes for my '95. One of them works and the other does not. I'm getting a little older so I can NOT see the FCC code on them but think 2 of them are the same. One that works and one that doesn't. The one that doesn't had a unlock button that didn't click. So I opened it and found some green waxy stuff all over that button. I put an ohm meter on a few of the contacts and did not get any flow. So I cleaned off the stuff which didn't help much so I put a soder iron on it and the stuff leaked away. So I checked it again with the ohm meter and it let current flow good, like the other button.

But I still could not get it to program with the "key 5 times" process. IDK, but don't want to give up.