Hi so the RD on my Di2 DA has stopped working, FD still working. Battery is fully charged, and both levers show a solidd green light when i hold in the shift buttons, which makes me think the shifters are fine. When I hold the junction box in to finetune the light flashes red once and thats it. It does not go into fine tuning mode. Ive also tried plugging the RD cable in and out, any other ideas?

Can anyone help?

First, look over all wires and plugs, looking for abraded areas, any zipties that may be too tight on them, causing a break. Then I would pull all plugs and look for corrosion, clean, put a touch of grease on the plastic for sealing, and plug it back in.
If that doesn't reveal anything, take it to a shop with the diagnostics box.
Internal wires or external? if internal, there are 4 more plugs inside that rely on heavy duty heat shrink for sealing. I've seen some people leave theirs off, with consequences.

Any crashes? One RD stopped signaling to the FD of its position, so the FD no longer trimmed, after a pretty big crash. so if you know someone w another RD, that's something to check. If you know someone with another di2 bike, you could easily plug your stuff into his to locate the culprit.

Hmm tried all that and still cant get RD to work.

All the local bike stores in Brighton, UK, dont seem to have a clue about Di2. Certainly none have the Di2 diagnostics kit. Anyone know where I could find a shop that has it?

Or anyone from Brighton, perhaps I could try plugging my rear derauileur into another set-up to see if it works? That way I could eliminate the possibility that the RD is dead. Could be the interternal junction box, can someone explain how/iof I could test that. I now have access to it and looks like it is soldered togtther rather than plugged in like the other external components?

Any adivce much appreciated.

Oh also, if the RD was in crash protection mode, how can i tell and how would i get it out of that state? Is it safe to force the RD to the middle of the block, current its in the 27! Could do with in the 15, at least then I could turbpo for now.

Cheers,