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repairing broken W202 Key fob.

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by anyweb, Apr 2, 2007.

  1. anyweb

    anyweb Senior Member

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    Your Mercedes:
    w213,w120 (petrol),w120 (diesel)
    hi all, I'm posting this incase any of you have a similar problem, sure saved me some bucks and only took an hour or so to fix.

    This how-to is mirrored here > http://www.niallbrady.com/mycar/c220/fixkey.html

    Problem:-

    * key won't open the car
    * key LED won't light even with known good batteries
    * chance that you may have dropped the key recently

    Solution:-

    In my case, the solution to the problem became evident when I took the key apart (it should prise apart quite easily, if not use gentle force), as a piece of it fell to the floor when I got the two halves open. The piece that fell on the floor was an electronic switch which had become loose from its 4 soldered leg joints.

    So what do you need to accomplish this ?


    * steady hand
    * bright light
    * a magnifying glass to see the solder joints etc..
    * a soldering iron
    * some solder wire

    (see below)

    [​IMG]

    Here is my broken key in it's disassembled state.


    [​IMG]

    You can see the switch is not attached to the circuit board, and thus, the key's infrared functions cannot work.

    I examined the detached switch with a magnifying glass and could see the legs were bent so I re-arrangfed them gently to be more in line with the 4 contacts on the circuit board (be gentle, if any of the legs snap off you are going to find it VERY hard to fix as they are so small).

    I then aligned the switch to it's mating points on the circuit board, at this point, I held it very tightly against the board and had my soldering iron heated up for the next stage, soldering.

    [​IMG]

    Once correctly aligned I carefully got a blob of solder on the end of the soldering iron and 'touched' it briefly to each of the 4 legs in turn until they clearly had solder in place. Be careful with the soldering iron, you could end up getting solder on any of the other contact areas around the switch and that wouldnt be a good idea as there are quite a few 'lines' running around it.



    Here's what they looked like after the soldering process

    [​IMG]


    Finally I had to reassemble the key at this point you can put the two batteries back in and you should see the familiar LED light up after a few seconds of pressing *SUCCESS*

    [​IMG]
    Please note:- when you have the key all back together again, you may notice that it doesnt 'flick out' as it used to, this is simple to fix, open the key again in two halves and 'wind' the key around its centre point ONE FULL TURN in the direction of force, then place the two halves back together again.


    One last note, after doing this job you'll have to RESYNC the key to your car, to do so, do as follows,

    press the button on the key while pointing it at the rear view mirror then insert the key in the ignition and turn it so that all the dash board lights light up, wait a few seconds then take it out of the ignition, press again and the GREEN or RED mirror led should light. If they both flash together at the same time then try again. If they continue to flash together then replace the batteries and try again, if they flash alternatly (red/green/red/green) then you may have some other problem like the car battery).

    cheers
    anyweb
     
    Last edited: Oct 31, 2007
  2. television

    television Always remembered RIP

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    What a genius you are with the brilliant photos and write up.

    it is possible to put an elastic band around the whole thing to hold the switch in place while you tack the first leg of the switch to the PCB.

    Tactile switches are available from all TV service centers if the legs are broken on the existing switch, they come in 3 types.

    Congratulations Niall .:-D :-D :-D
     
  3. OP
    anyweb

    anyweb Senior Member

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    thanks malcolm, it sure was a relief when the key worked after the soldering job !

    cheers
    anyweb
     
  4. television

    television Always remembered RIP

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    2000kr of relief, the pics are a joy
     
  5. Doyle

    Doyle Senior Member

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    i paid £120 for a new key a wee while back where was this guide then?!!!! lol

    nice guide mate very helpful and ill give it a go on my other broken key.
     
  6. OP
    anyweb

    anyweb Senior Member

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    did it work on your broken key ?

    cheers
    anyweb
     
  7. lovedove13

    lovedove13 New Registration

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    Key fob repair..WORKED!

    THANK YOU! One of my key fob cases opened easily and by following your instructions the repair is done and it works! :grin:The problem is I can't get the other fob case opened. I'm destroying the case just trying to pry it open. :confused: Is there a trick? If I can't get it open do you know where I can get an inexpensive replacement? I can't find one on Ebay. Thank you!
     
  8. OP
    anyweb

    anyweb Senior Member

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    Your Mercedes:
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    the previous owner may have glued it shut,

    just use force around the visible edges and it will come apart eventually,

    forget about ebay for replacements,

    cheers
    anyweb
     
  9. mhdgibbs

    mhdgibbs New Member

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    good description and very helpful both of my keys had this problem managed to bodge one back together so can use it as spare when ive bought new one from MB dealer
     
  10. television

    television Always remembered RIP

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    If you cannot close the case again,plumbers pipe solvent will glue it, do leave it overnight to set
     
  11. M30RCK

    M30RCK Active Member

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    Great post, many thanks..useful to know as the keys are hard to get hold of.
     
  12. W12421

    W12421 New Member

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    W202 Key Fob-Fix works for W124 also

    The symptoms sounded very familiar. Recently dropped my key to my W124 E280- following which it would not open the doors remotely. Changed batteries still no joy. Pressed the second spare key into action.

    Looked at this post and the pictures looked very familiar- dug out my duff key and prised it apart- took a bit of effort, looked to be some glue in far corner.

    Lo and behold two of the legs from the switch are detached!

    Just in process of soldering together will let you know if successful.

    Great post and just what makes this website so good. :D:D:D

    Many Thanks

    Martin
     
  13. bigasotonuk

    bigasotonuk Senior Member

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    Why are the keys hard to get hold of? I had no problem at all.
     
  14. W12421

    W12421 New Member

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    W202 Key Fob-Fix works for W124 also

    They may be available at a price? 20 minutes and a bit of solder and I'll treat myself to a pint of Guinness for a job well done!

    Ta Niall


    If you're ever in Belmullet I'll buy you a pint of Guinness. :D:D:D
     
  15. OP
    anyweb

    anyweb Senior Member

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    glad it helped !

    cheers

    anyweb
     
  16. Miserable Scotsman

    Miserable Scotsman New Member

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    Excellent article, I've now got 3 working remotes for my C180.... Thank you from Miserable Scotsman
     
  17. paradisej

    paradisej New Registration

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    Electronic Key Repair

    Hi, Anyweb,

    A million thanks to you for this posting. I owe you much. I followed your instructions, and it worked, and saved me NZD 500.00 from ordering a new set of key for my 1995 C220. It's generous bloggers like you that makes it all worthwhile.

    Kind regards,

    paradisej
     
  18. Fakhar

    Fakhar New Registration

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    How do i actually open the remote?????

    Hi, could someone out there guide me to open the remote before i do all the bits shown on the pictures.....................sorry if i am being daft..............Cheers
     
  19. OP
    anyweb

    anyweb Senior Member

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    Your Mercedes:
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    use a knife (pen knife would be suitable) or flat blade screwdriver to prise the two havles apart

    if they don't come apart easily they may have been superglued by a previous owner, in that case, use force

    cheers
    anyweb
     
  20. mm3275

    mm3275 New Member

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    Absolutely brilliant post, most useful
     

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