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[iSurgeon]

 Has anyone ever had this issue?
I bought a 2015 fx used last summer. Currently has about 1k miles. It has always worked perfectly until a few days ago I turned it on to take a quick ride and all 12v features were dark but the bike drove normally. Did some searching and found the hidden high voltage fuses for the mbb and the dc/dc converter. MBB fuse fine DC/DC fuse was bad. Next morning went out to get a new fuse, replaced it with both batteries removed, put batteries back in and nothing. No signs of life whatsoever when the key id switched on or if the charge cable is plugged in. Checked both fuses again and they are both fine. Tried removing the dc/dc fuse, tried unplugging the dc/dc altogether, removed mbb and reinstalled, the mbb does have pack voltage and ground on the correct pins at the harness and it gets 11.8v at the harness when the key is switched on still nothing.
I called zero and they said to bring it to a dealer which is 4hrs away.

Everything points to a bad mbb but not sure why or how that would happen. If anyone has any ideas or recommendations before I order a new mbb I would appreciate it. I'm going to test the dc/dc today to see if it is operating properly.
Thx, Tommy.

[BrianTRice@gmail.com]

The DC converter may be the primary fault here, but sometimes the onboard charger as it fails triggers faults in other components.

Here's the unofficial guide to the DC converter:
https://zeromanual.com/wiki/Unofficial_Service_Manual#DC-DC_12V_converter

It is separately purchasable, and I've replaced one myself on a DSR. I assume that on an FX it's much easier since there's less to remove.

Do check the connector for dirt and grime which, when wet, can cause electrical faults that degrade its functionality until it fails. Sevcon, who makes this converter, have not sufficiently protected that connector from ingress of moisture and dirt.

[Auriga]

It is possible for the DCDC to fail, and damage the MBB and/or blow the low power b+ fuse as well.

The dealer can check MBB operation, and sometimes Zero will give you a discount on one or both replacement parts.
I'd recommend taking it in.

If the DCDC is bad, replacing the MBB would blow it again anyway,

[BamBam]

This worked for me when my 2017 DSR went dead.

http://electricmotorcycleforum.com/boards/index.php?topic=7963.msg67117#msg67117

[iSurgeon]

Ok so I just received a replacement mbb. Installed it and no change, still no sign of life at all. Voltage on the power in wire to the mbb is 104v then drops to 26v when I turn the key to on. Whats next? BMS

When I try to get the contactor to close like this the bms thinks it is colsing the contactor but its not actually closing(connected to it with obd cable and putty app.) .

[Auriga]

Dude, I'd stop doing that right now and take it to a dealer. You've already provided enough evidence to void your warranty, and Zero reads these forums. Plus each of those batteries is 3k+ to replace, if you break it

Something non obvious is wrong, and we don't have all the documentation and tools required sometimes.

Props for keeping at it this long though. 

[iSurgeon]

Dealer is 5 hrs away, and I'm out of warranty. Somehow my 15' fx has 14' batteries.

[iSurgeon]

Also would add, the dc/dc was bad and is no longer in the system. Trying to figure everything else out before replacing.

[BrianTRice@gmail.com]

The Sevcon DC-DC converter is available generically. Check the part number on the side (300W or 500W option for the correct voltage range) and google it to see what stores can provide it reasonably.

I've replaced mine on my DSR as an exercise.

[iSurgeon]

Thanks Brian, I found the Sevcon 500 watt dc/dc on ebay for $157.50

Yesterday I found that the 10a smd fuse on both of my BMS boards are bad. Seems the dc/dc took them with it when it died.

[NEW2elec]

That's the guy I got mine from.  Works fine and came in a nice anti static plastic bag.  Be sure to get the aluminum tape for it as well.

[Auriga]

The DC DC can certainly wreak a lot of havoc if it fails. I'd recommend putting some heat shrink or additional waterproofing around the connector on it. Usually helps if you get error codes while it rains too.

[iSurgeon]

So it turns out the dc/dc damaged the bms boards in both batteries when it failed. On both there was a blown 10 amp surface mount fuse which I got replacements from mouser and soldered on. One battery is good and the bike works, the other bms has more issues. Does anyone have a schematic for the bms ? Part number is 41-06419.

My MBB was fine so I'll be listing the extra in the for sale section.

[BrianTRice@gmail.com]

If that surface mount fuse is on the precharge circuit, it's a known issue and it would be an interesting effort to get it replaced.

Reference:
https://zeromanual.com/wiki/Unofficial_Service_Manual#BMS_Parts

[iSurgeon]

It's not the pre-charge fuse as marked in pink on that page but it's the same size and part number. The fuse I replaced is just under the right side of the top black connector plug.