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Disassemble remote control to fix intermittent keys

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    JohnH77

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    How do I disassemble the RM-L03 remote control?

    There are no screws in the battery compartment so I assume it is just spring lugs on the plastic top and bottom but it is quite difficult to see where they are.

    Several of the frequently used keys are intermittent and I need to fix them.

    Sat 17 Aug 2019 14:13:49 #1 |
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    JohnH77

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    Done it.

    The "lower grey part" and the "upper black part", both on the top, are separate.

    Insert a thin knife under the grey_part corner and gently prise it up while also pulling the black_plastic_bottom_wall outwards to free the spring catches. Once the grey_part has been lifted slightly at the corner it is easy to slide the knife edge downwards into the black plastic base and to ease it outwards to free the catches. The "clips" are on the black_plastic_base and they spring into recesses in the lower_grey_part. There are three catches along the grey_part side and two along the bottom.

    Remove the black_top by easing the bottom_side_wall away at the red button and working along towards the top. Repeat starting at the blue button. There are four catches along each side and two along the top.

    You can now lift off the rubber_button_tops to get access to the contacts.

    I shall be sticking small circles of aluminium_foil_with_one_side_sticky to the underside of the rubber key tops to ensure good contact with the PCB switch contacts to fix intermittent keys.

    I know I can buy a replacement but I like fixing things!

    Sat 17 Aug 2019 15:09:44 #2 |
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    batteryman

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    I have opened and cleaned several Humax remotes of different types and one thing I found is they open much more easily when they're warm. A sunny window ledge usually works but I've resorted to a microwave combi oven set on convection at 40C in winter!

    I usually wash the rubber keypad with warm water and a well known brand of washing up liquid followed by a thorough rinse and dry (the sunny porch works well).

    The contacts usually clean up ok with isopropanol cleaning fluid and a tissue - keeping well away from the integrated circuit on the board. It dries quickly and doesn't leave any residue.

    Final job is to thoroughly clean the case and cursor inserts - they can have all sorts of food and human residues on them. Snap everything back into place, press the pvr button on the ones that have it and they're usually back to normal.

    Sun 18 Aug 2019 14:04:35 #3 |
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    JohnH77

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    Thanks for that.

    What you have written suggests that the keys become intermittent / need more force to work because the surfaces get dirty and cleaning the surfaces is all that is needed.

    I had always assumed that the keys become intermittent / need more force to work because the rubber loses its conductivity. I therefore cut small disks of sticky-back-aluminium-foil and glued them to the rubber keys to provide a new conductive surface. This worked well on all keys except the OK key and the eight surrounding it where the contact part was only about 2mm in diameter and it was difficult to get the aluminium foil to stick to it.

    I refurbished my burglar alarm keyboard in the same way a few years back and it has worked well ever since.

    But just cleaning the contacts is much easier!

    Sun 18 Aug 2019 14:37:42 #4 |
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    jaeger

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    There are various conductive paints available I've seen used on the rubber key pads - Amazon, RS components etc sell them.

    https://tinyurl.com/y3uqtbnv

    https://tinyurl.com/y5gj4jag

    Mon 19 Aug 2019 6:52:29 #5 |
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    JohnH77

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    Another thought. When I strip down rubber keyboards like this there seems to be a thin black grease inside between key and contact.

    Is this a genuine grease which I should leave in place?

    Or is it "collected gunge" which I should get rid of as batteryman does?

    Mon 19 Aug 2019 10:05:05 #6 |
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    jaeger

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    I've never seen any grease used between the rubber pad and PCB, It might well be the conductive coating that has worn off the membrane.

    Tue 20 Aug 2019 4:56:05 #7 |
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    batteryman

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    The insides generally collect oils from the skin after a while and this can oxidise to form a greasy, waxy substance similar to earwax. Sounds horrible but we all exude a bit of greasy stuff from time to time!

    The black grease sounds like skin oils/conductive rubber debris. As far as I can tell, the conductive black rubber is not a coating, it's the whole keypad - much easier to manufacture as a whole thing in the same rubber with coloured bits inserted for the coloured keys.

    Tue 20 Aug 2019 18:57:17 #8 |
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    jaeger

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    The membranes have a conductive coating on a rubber pad, that's why they wear, I've seen temporary repairs done with a soft pencil.
    Years ago manufactures used to supply all the spares for R/C we used to repair them, replacements were only for lost or smashed units.

    https://en.wikipedia.org/wiki/Silicone_rubber_keypad

    Tue 20 Aug 2019 21:17:19 #9 |
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    JohnH77

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    jaeger

    Thanks. I checked out that document and did some follow op searches and nothing mentions any grease when talking about rubber keyboard design.

    I think the "grease" must therefore be gunge which should be cleaned off. Just doing so may be enough to fix the keys but, if not, adding a conducting surface like aluminium foil or conductive paint definitely fixes it.

    Sun 25 Aug 2019 9:55:24 #10 |

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