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di2 6870 rear derailleur doesn't work, junction box doesn't show lights

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di2 6870 rear derailleur doesn't work, junction box doesn't show lights

Old 06-17-22, 06:52 AM
  #1  
mattkime
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di2 6870 rear derailleur doesn't work, junction box doesn't show lights

My rear derailleur stopped working in the middle of a ride yesterday. Nothing happened, no crash, it just stopped working. The 'junction a' box doesn't seem to respond to button presses either. I can shift the front derailleur just fine. I've tried clearing crash mode, I've tried leaving it unplugged, and I've tried charging it, no change. I tried using E-TUBE via windows but it failed to connect BUT it was my first time trying to use it so its possible that there's something wrong with that setup. Disconnecting the rear derailleur does _not_ restore junction box a functionality.

At this point I lean toward a battery or junction box problem.

Any tips on resolving this? I'm out of ideas.

Last edited by mattkime; 06-17-22 at 07:05 AM.
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Old 06-17-22, 07:56 AM
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Plug the RD into the FD E-TUBE wire, and try shifting the RD.

As for connecting your Di2 charger to a PC, the latest E-TUBE software does not support the use of a charger, you have to use Shimano’s dedicated (non-charging) PC interface or an old version of E-TUBE software with your charger.

Edit
Ok, you got me interested… I got outta bed, went downstairs and unplugged my RD (8000 series)
FD still functions.
Holding a brifter does cause junction to flash battery level and mode.

Last edited by Barry2; 06-17-22 at 08:06 AM.
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Old 06-17-22, 09:08 AM
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The fact one shifter works and nothing else including the lights on your junction box is puzzling.

I'd probably go back and unplug then plug back in every wire connection from the battery to the junction box or vise versa. Some connections are hard to find and you have to undo one end and pull the other out of the frame. But don't lose that loose end in the frame.

Check on that shifter that is working. Sometimes two wires are connected to them. Is one loose that goes to the junction box?

Your eTube software does show you what components it sees. So if it didn't show you anything it might be the wire on the junction box that the battery is also on. Try it again. Take a pic of the screen and post it.

Last edited by Iride01; 06-17-22 at 09:12 AM.
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Old 06-17-22, 09:27 AM
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IME (3 episodes of a derailler malfunction) all were due to cable problems: two for apparently good plugins of cable ends
that were not, it turned out that there are two 'pops' or 'clicks' when one seats a connector and only the second click
confirms the electrical connection. These two occurred: once when the bike fell over and the R brifter rotated in on the bar
and once when I hit a really bad bump and the R brifter again slid down slightly on the bar. The 3d fail was unrelated to
any incident but an RD stopped working and after an etube eval showed no connection, a cable substitution fixed the
problem. My local Di2 guru has found over the past 8 yrs that a bad connex or occasionally a bad cable is almost always the problem
when a malf occurs.
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Old 06-17-22, 03:08 PM
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I removed the rear derailleur and connected it via an additional cable to my five port junction a box. Works fine. Looks like its a cabling problem.
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Old 06-17-22, 03:41 PM
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Barry2 
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Are you able to move the existing RD cable run to the proven functional port on the junction box?

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