Error 07h on BBS02 - fried controller?

Hi there,

I recently had intermitent occurences on my BBS02 750W where my C965 display would indicate the error code « 07h » randomly in the middle of a ride. When this happened there would be no power output. After I had this happened 2-3 times in a week, it became a persistent issue and it was not possible to get any power from my mid-drive anymore.

Since the « 07h » error code a overvoltage protection error, I started checked my voltage, and the output tension from the battery was below 58.5volts, with all cells properly balanced (could check with the bluetooth-enabled BMS).
I observed connectors with no signs of shorts.
I plugged a programming cable in in place of the C965 and was still getting no power, ruling out a display issue.

It was time to open the body for the first time and take a look at the controller.

The picture below shows what I found.




There was a white residue all over the aluminium inner casting, a bit like the oxidation residue you'd get on batteries that have been exposed to moisture for a long time. Also on the second picture you can see a green oxydation power near the top (close to that screw holding the small flange holding the cables in place). Could it be that a capacitor blew out from there, creating all this green and white oxidation residues?
I did submerge the unit on a heavy rain about 6-months prior to having issues so thought this could be related.
I also realised that the multi-wire harness had been pinched flat between the unit and the bike.

I already ordered a new controller but would appreciate any first diagnosis from others. Also, is there anything I should be doing before putting it in to avoid potential damage to it in case my analysis is wrong (and there's an issue outside of the controller)?

error 07h in the instruction is written "overcurrent". Perhaps some 18650 element is damaged, because of this there is a sharp current drop. When I replaced the battery the error went away.

It looks like water got into the housing and damaged the board. You may be able to dig away some of the grey potting around the green spot and try cleaning it up with a stiff brush and a little water. Since your error is intermittent, there's a good chance nothing is blown, just some conductive residue bridging traces on the board. Once it looks clean, make sure it's completely dry and test the motor. If it works properly, use something to coat the unpotted spot to make it waterproof.