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Thread: Fried diode board!!!

  1. #1

    Exclamation Fried diode board!!!

    Ugh. One thing after another it seems with these bikes.

    I arrive to work on my bike and its smoking like crazy from the starter cover.
    Check the front charging system and sure enough the diode board is toasted! melted even.
    I read somewhere on here the same thing happening to someone but it was due to a faulty diode? or running to many high-wattage lights on his bike? i wasn't sure.
    I did upgrade the system to the 3 phase one from EME a year ago about but looking for any insight as to why it might of got toasted like this.
    Also can I remove it or disconnect it and ride it back home safely? I understand the diode just converts ac to dc or is it the other way around? ha
    so there would be no charge but im hoping there should be enough charge in the battery to at least get it started and going.

    IMG-0728.jpg

  2. #2
    Liaison 20774's Avatar
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    What's bike year and model?

    I'm not aware of any diode issues with the aftermarket board. You would need to get back to the seller on that.

    Yes, provided there are no serious shorts, you don't need an alternator to ride the bike as long as there is enough battery power left. I'm sure there are some wires that would be beneficial to unplug. From the diagram, I'd pull everything is connected to the alternator. Also it looks like the one/two wires on B+ on the diode board...these are on the upstanding terminals that feed back to the battery. Tape everything so it doesn't touch ground. Again, you have an aftermarket board, so until someone with familiarity with this or input from the seller, be careful.

    Try things with the cover off and see if the engine runs without any smoke from the area.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3

    Diode Board

    Quote Originally Posted by s_alt View Post
    Ugh. One thing after another it seems with these bikes.

    I arrive to work on my bike and its smoking like crazy from the starter cover.
    Check the front charging system and sure enough the diode board is toasted! melted even.
    I read somewhere on here the same thing happening to someone but it was due to a faulty diode? or running to many high-wattage lights on his bike? i wasn't sure.
    I did upgrade the system to the 3 phase one from EME a year ago about but looking for any insight as to why it might of got toasted like this.
    Also can I remove it or disconnect it and ride it back home safely? I understand the diode just converts ac to dc or is it the other way around? ha
    so there would be no charge but im hoping there should be enough charge in the battery to at least get it started and going.

    IMG-0728.jpg
    From the photo, it appears that the mounting bolts are missing? If one of the two on the right side of the picture backed off and touched the red wires, I'm guessing that would short 12v to ground and cause the problem.

    I have the same diode board on my R90s and it's been totally trouble free for over 10 years. I did apply blue loctite to the four hex head nuts, btw.

    RPGR90s

  4. #4
    Quote Originally Posted by 20774 View Post
    What's bike year and model?

    I'm not aware of any diode issues with the aftermarket board. You would need to get back to the seller on that.

    Yes, provided there are no serious shorts, you don't need an alternator to ride the bike as long as there is enough battery power left. I'm sure there are some wires that would be beneficial to unplug. From the diagram, I'd pull everything is connected to the alternator. Also it looks like the one/two wires on B+ on the diode board...these are on the upstanding terminals that feed back to the battery. Tape everything so it doesn't touch ground. Again, you have an aftermarket board, so until someone with familiarity with this or input from the seller, be careful.

    Try things with the cover off and see if the engine runs without any smoke from the area.
    1981 r100t I believe.

    thank you for the insight.

    I reached out to EME to see what they think

  5. #5
    Quote Originally Posted by RPGR90s View Post
    From the photo, it appears that the mounting bolts are missing? If one of the two on the right side of the picture backed off and touched the red wires, I'm guessing that would short 12v to ground and cause the problem.

    I have the same diode board on my R90s and it's been totally trouble free for over 10 years. I did apply blue loctite to the four hex head nuts, btw.

    RPGR90s
    Yeah, it would appear I might of missed a bolt when I reinstalled it last after redoing the timing chain replacement.
    Shoot.
    Thank you for the input.

  6. #6
    Tried to reconnect the red wire that comes from the starter with the battery connected and bike turned off and it immediately started to turn red and heat up in that corner near the lower stud. still confused though

  7. #7
    Liaison 20774's Avatar
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    My guess is that red wire is straight from battery positive and you're hooking it up to something that has become grounded due to the meltdown. I suggested not connecting that wire. Normally that wire is what is used to supply the battery with output from the diode board...it just goes to the starter as a piggyback on it's way to the battery. Since things are messed up, it doesn't work that way now.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  8. #8
    Quote Originally Posted by 20774 View Post
    My guess is that red wire is straight from battery positive and you're hooking it up to something that has become grounded due to the meltdown. I suggested not connecting that wire. Normally that wire is what is used to supply the battery with output from the diode board...it just goes to the starter as a piggyback on it's way to the battery. Since things are messed up, it doesn't work that way now.
    Right. I just wasn't sure how the bike could start without that wire connected. Ive decided just to leave it at work in the garage till I can get a new diode with wiring next week hopefully

    I should add that i'm using a lithium battery with an adjustable regulator

  9. #9
    Registered User ebeeby's Avatar
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    IIRC Didn't someone write recently about bad isolators from EME? And EME knew the problem and sent new ones and were very helpful?

    1) First thing to go is memory
    2) Can't remember what the second thing is
    1973 R75/5

  10. #10
    Liaison 20774's Avatar
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    Brook had a discussion about the EME charging system on his 1983 R100RS build:

    https://forums.bmwmoa.org/showthread...=1#post1192750
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  11. #11
    Unregistered User dduelin's Avatar
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    The only time I had a shorted board was when one of the rubber mounts sheared and in the jiggling of riding on a dirt road the board touched the bare metal engine cover (1981 R100).
    Dave

    GL1800
    R 1200 RT

  12. #12

    Diode Board

    Quote Originally Posted by dduelin View Post
    The only time I had a shorted board was when one of the rubber mounts sheared and in the jiggling of riding on a dirt road the board touched the bare metal engine cover (1981 R100).
    Yep, that's why they sell solid mounts as an upgrade over the rubber. The original rubber mounts were cracked and failing on my R90s. Very glad I changed out to solid units.

  13. #13
    Registered User STEVENRANKIN's Avatar
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    solid mounts

    Solid mounts also aid in grounding. That is the reason I have been told all of the replacement diode boards recommend solid mounts. Does not hurt that the cracked mount problem is solved either. St.

  14. #14
    Registered User Guenther's Avatar
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    With solid mounts the vibrations go straight to the electronic board. Besides cracking the board it may shake out some poor solder points for the diodes.

    I think that's why BMW used...rubber mounts.

    /Guenther

    Edit: spelling/wording last line
    Last edited by Guenther; 08-05-2020 at 10:50 PM.
    2017 F700GS - I wish she had a drive shaft

  15. #15

    Diode Board

    Quote Originally Posted by Guenther View Post
    With solid mounts the vibrations go straight to the electronic board. Besides cracking the board it may shake out some poor solder points for the diodes.

    I that's why BMW stater with...rubber mounts.

    /Guenther
    But, my '73 /5 had solid mounts and was original with over 150k. I'm sure opinions vary as to why they went with the rubber units, but never had an issue with solid mounts on all my Airhead's.

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