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Thread: Success in General Module Repair

  1. #1
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    Success in General Module Repair

    So evidently I did not fry the board attempting to repair it - Thanks so much to everyone who chipped in with good advice and knowledge. I hadn't found a walkthrough with pictures, so I figured I'd post something up for those a little nervous about embarking on the repair.

    First off, I got my capacitors from Newark - part numbers in this thread: http://forums.bimmerforums.com/forum....php?t=1595968

    Step the first: Disconnect the negative battery terminals in the trunk!

    Everyone told me to remove the knee bolster to get the general module out and I can't imagine anyone getting it out without doing so - I am a firm believer in taking stuff out if it's in the way. First remove the trim piece - it is held on by some push/pull studs and some velcro



    To remove the bolster itself, there are a couple of screws and 4 bolts (two of which are partially hidden behind the trim above it. See the pictures for the locations



    The general module is between the steering wheel and the drivers door in a stack of three. The one that you want is in the middle. Remove the Body Electronics module first to give yourself some room. I disconnected all the harnesses (rotating locking connectors) first, and then rotated the modules out as shown to avoid the metal bracket on the side. The modules are held in place by tabs on each side - just bend them back.



    Once you have the module out, you can pull back the tabs on each side and remove the PCB from the casing. The capacitors are the five canister shaped pieces - note the orientation - the new capacitors must go back in the same orientation.



    Removing the old capacitors was the hardest part of the job for me, as I had never done it before. After listening to a bunch of people and reading what I could on the net, and several hours of messing around getting frustrated with the board, here is my advice on those trying it for the first time:
    1) EEDegreeToDrive is right - get a decent temperature controlled soldering station, a Radio Shack soldering gun is going to mess up your board
    2) Take good care of your tip - clean and re-tin the tip more often than you think you should (like between every junction)
    3) The coating on the board was causing lots of problems - I would remove the solder, and the coating would hold the cap in place (and I didn't realize it for a while - which led to me probably putting more heat into the board than I wanted to). Free the cap from the coating by mechanical means if possible (X-acto knife and some scraping in my case) - I don't know if acetone or something similar would work to dissolve it
    4) Start out by re-soldering the junction over top of the old one, then bring the iron in and re-melt the entire glob - while the solder is all melted, use pliers from the other side of the board, and pull the leg of the capacitor out. Then you can melt the solder from one side of the board, and use a solder sucker from the other side and get the whole kit and caboodle in one shot.

    I'm sure the experts will correct my lousy technique, but this seemed to work the best in my case. Solder the new capacitors in place, ensuring that you have the correct polarity. Installation is the reverse of removal. I re-attached the negative battery cables before the bolster and trim panels to be sure the repair worked (now, however, the radio is complaining about needing a code - anyone know how to get the radio code?)

    You're all done - go get a beer.

    (almost forgot the most important step - be sure that you have a capable assistant. Here's mine )

    Attached Images Attached Images
    Last edited by Spandrel; 04-24-2019 at 08:35 PM. Reason: Replaced missing images

  2. #2
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    Awesome way to contribute, Great post Spandrel!

  3. #3
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    Thanks for the pictures of the knee bolster! I've heard a lot about it, but this is actually the first time I see it (European E31 do not have it).

  4. #4
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    Nice write-up Spandrel. Thanks!

    Tony

  5. #5
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    Thanks, think I will be looking at doing this day.

  6. #6
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    you have to get the code from the dealer, from everything i've read. seems i've heard there may be an identifying sticker on the radio somewhere. i like most just ditched the radio.
    Last edited by m10n; 02-09-2012 at 10:59 AM. Reason: wrong

  7. #7
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    You can get the code from the dealer or you may want to check your owners manual if you have it. The former owner of my 8 and my 7 series had written the radio code in the book.

  8. #8
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    Quote Originally Posted by toomann View Post
    You can get the code from the dealer or you may want to check your owners manual if you have it. The former owner of my 8 and my 7 series had written the radio code in the book.
    +1

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  9. #9
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    Quote Originally Posted by Spandrel View Post
    Everyone told me to remove the knee bolster to get the general module out and I can't imagine anyone getting it out without doing so - I am a firm believer in taking stuff out if it's in the way. First remove the trim piece - it is held on by some push/pull studs and some velcro

    To remove the bolster itself, there are a couple of screws and 4 bolts (two of which are partially hidden behind the trim above it. See the pictures for the locations

    Removing the old capacitors was the hardest part of the job for me, as I had never done it before. After listening to a bunch of people and reading what I could on the net, and several hours of messing around getting frustrated with the board, here is my advice on those trying it for the first time:
    1) EEDegreeToDrive is right - get a decent temperature controlled soldering station, a Radio Shack soldering gun is going to mess up your board
    2) Take good care of your tip - clean and re-tin the tip more often than you think you should (like between every junction)
    3) The coating on the board was causing lots of problems - I would remove the solder, and the coating would hold the cap in place (and I didn't realize it for a while - which led to me probably putting more heat into the board than I wanted to). Free the cap from the coating by mechanical means if possible (X-acto knife and some scraping in my case) - I don't know if acetone or something similar would work to dissolve it
    4) Start out by re-soldering the junction over top of the old one, then bring the iron in and re-melt the entire glob - while the solder is all melted, use pliers from the other side of the board, and pull the leg of the capacitor out. Then you can melt the solder from one side of the board, and use a solder sucker from the other side and get the whole kit and caboodle in one shot.

    I'm sure the experts will correct my lousy technique, but this seemed to work the best in my case. Solder the new capacitors in place, ensuring that you have the correct polarity. Installation is the reverse of removal. I re-attached the negative battery cables before the bolster and trim panels to be sure the repair worked (now, however, the radio is complaining about needing a code - anyone know how to get the radio code?)

    Nice job, nice writeup! Some brief points about having the right tools for the job...

    1. It comes out easy enough without removing the knee bolster... Less than 10 minutes
    --You need a flashlight and to be able to lay on your back looking up at the modules
    --You need 1/4" drive socket and a 6" extension to get the three nuts/bolts and drop the three modules down. A flathead screwdriver in the 1/4" socket works quite well too..
    --Once "free" and it falls down a little, the connectors can be slid over/disconnected

    2. To remove the caps:
    --you can just cut them out with diagonal cutters, then wiggle them side-to-side to break the conformal coating.
    --Then use your iron (and extra, fresh solder) to pull out the remaining leads, they will usually come right out on the tip of your iron when you use fresh solder liberally
    --Then clean the holes with a solder sucker. (They're like $10-$15) You can also heat the pad and blow on the hole to 'open' the solder. Alternatively, solder braid can be used.
    --Once the holes are clean, the new caps drop right in

    (Side note/edit: For bigger things like relays/connectors, First renew solder joints with iron and fresh solder. Then, a heat gun, a tap on the desk, and gravity work like a charm)

    3. If you have to use a combination of soldering and pulling, be gentle and don't force anything. Also, use fresh solder to remove the old parts. It may seem counter intuitive to add more solder, but the rosin core (flux) helps the old solder flow easier.

    4. I also pulled mine without pulling the battery terminal IIRC. Also, I changed the capacitors one at a time and it didn't lose any memory. (I likely just got lucky)
    Last edited by EEDegreeToDrive; 03-19-2012 at 03:42 PM.

  10. #10
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    Quote Originally Posted by EEDegreeToDrive View Post
    Nice job, nice writeup! Some brief points about having the right tools for the job...

    1. It comes out easy enough without removing the knee bolster... Less than 10 minutes
    --You need a flashlight and to be able to lay on your back looking up at the modules
    --You need 1/4" drive socket and a 6" extension to get the three nuts/bolts and drop the three modules down. A flathead screwdriver in the 1/4" socket works quite well too..
    --Once "free"ad it falls domn a little, the connectors can be slid over/disconnected

    2. To remove the caps:
    --you can just cut them out with diagonal cutters, then wiggle them side-to-side to break the conformal coating.
    --Then use your iron (and extra, fresh solder) to pull out the remaining leads, they will usually come right out on the tip of your iron when you use fresh solder liberally
    --Then clean the holes with a solder sucker. (They're like $10-$15) You can also heat the pad and blow on the hole to 'open' the solder. Alternatively, solder braid can be used.
    --Once the holes are clean, the new caps drop right in
    I hadn't thought to look to see if the module container would come out - the knee bolster only took about 20 minutes without knowing about the hidden bolts, so not too bad either way.

    Great tip on cutting out the caps and then just working on the remaining leg in the junction - that would certainly have made it easier, and it did go much quicker once I figured out that a 'liberal' amount of fresh solder made things so much easier.

    Many thanks for the advice!

  11. #11
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    Wink capable assistant

    Great write up!

    I really like your capable assistant!

    Ken

  12. #12
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    I would never have figured out how to remove the knee bolster without your write-up and pictures. Thanks very much for documenting and sharing the process. I also like your cute assistant
    1991 BMW 850i / V12 5.0L [M70] / ZF4HP24 E/H

  13. #13
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    Just a thanks Spandrel for the write up and photos. Just completed this and the info on the knee bolster removal helped a lot.

    Also, thanks Steffen for the Euro programing of the light module. Killed two birds with one stone while I was under the dash.

    Mike

  14. #14
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    This made my job so easy! Pulled the laptop out into the car, and voila! It was out, I have the parts needed, just waiting for the next 3 night shifts to go by then I can work on it

  15. #15
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    Nice job. I did this a few years ago and wish I woulda had this write-up. Hopefully I won't need to do it again

  16. #16
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    I just did it today. I found the first two then third by console.fourth fooled me for a while but I knew it was upthere by the pivot point.You have to pull back some off the lower dash. When I did it w/o removing the bolster the hardest thing was getting the cables back on.Great write up and if I run out of GM I will try it. I have 3 now so I think I am safe for a while.
    97 840ci-99 540i6-90 535i5 all black

  17. #17
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    nice write up. love the assistant

  18. #18
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    Just wanted to thank Spandrel for the great write-up as I performed this General Module update today.

  19. #19
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    GM rebuild

    Thanks to Spandrel for the great info. Did my caps install today and it turned out good.The only difference was I used Digi-key for the parts.here are the numbers:
    cap -1uf alum 63 volt 20% axial --4062phct-nd $1.19
    cap -10uf alum 63 volt 20% axial --4066phct-nd $1.19
    cap-47uf alum 25volt 20% axial --4031phct-nd $1.31
    cap -100uf alum 25 volt 20% axial --4032phct-nd $1.28
    cap-470uf alum 40 volt 20% axial -- 4054phbk-nd $2.07

    total +$7.04 + shipping

  20. #20
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    What types of symptoms would be brought on by a failed/damaged GM?

  21. #21
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    Quote Originally Posted by BobieM View Post
    What types of symptoms would be brought on by a failed/damaged GM?
    +1 ?

  22. #22
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    Quote Originally Posted by BobieM View Post
    What types of symptoms would be brought on by a failed/damaged GM?
    - sunroof failure
    - window operation intermittant
    - car does not go into "sleep" mode (battery drain)
    - wiper malfunction

    Generally these things happen when the outside temperature is lower (i.e. winter), this is because of failed capacitors/solder joints.
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  23. #23
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    Quote Originally Posted by TxGR8White View Post
    - sunroof failure
    - window operation intermittant
    - car does not go into "sleep" mode (battery drain)
    - wiper malfunction

    Generally these things happen when the outside temperature is lower (i.e. winter), this is because of failed capacitors/solder joints.
    Ok. My cars windshield wipers, windows, sunroof, power door locks, and interior lights work when they want to. I haven't noticed a battery drain; however the previous owner owned it for 4 months and 2k miles and replaced both batteries. The previous owner also said he replaced the GM on the drivers-side door sill and I was told that it was actually the A5 Relay module by a member on here. Before the previous owner replaced the Relay Module he said the windshield wipers, windows, sunroof, power door locks, and interior lights didn't work, but after he put in the Relay Module, that is when they worked intermittently.

    I was told that it was the GM, or faulty capacitors that is cause my electrical gremlins, but is it possible that it could be anything else? I just want to make sure what my problem is before I start putting money into the problem.

    I also notice that my headlights pop out completely when turned on, or in some situations they will only pop the right side; or the left so it looks like the car is winking at you. This it irritating because sometimes the right side Headlight won't go back down when I turn my lights off.

    I apologize for the long post. I tried to break it down as much as possible but I wanted to put down all the info for a more accurate solution.

    Thanks
    Last edited by BMW3nthusiast; 08-03-2012 at 04:07 AM. Reason: Automerged Doublepost
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  24. #24
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    Thanks for the responses. It'll be great to have this tutorial, should something happen to it. I can always use soldering skill tuning

  25. #25
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    Quote Originally Posted by TxGR8White View Post
    - sunroof failure
    - window operation intermittant
    - car does not go into "sleep" mode (battery drain)
    - wiper malfunction

    Generally these things happen when the outside temperature is lower (i.e. winter), this is because of failed capacitors/solder joints.
    Well...
    That all sounds about right.
    Thanks to Spandrel for the thread and everyone else for posting.
    Kind Regards

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