What makes this happen? how do I not do it again? 
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Do those burn marks go all the way to the brass insert? Do they go even farther? It’s hard to tell. Is the mosfet split in half?
Damn. Is there burn marks on the brass insert?
Brass insert?
The brass circle on the top.
I’m supposed to be asleep. More later. :). Thx for looking / helping
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wish I could help, Fess, but I got nuttin’… and I need to go to bed…
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questions I’m pondering as a result of this mess.
Any reason not to run a 1.7 and 1.6 focbox together?
The original pair of focboxen were 1.7. I have a pair planned for another board that are 1.6 which i can steal to fix this board.
what’s the difference between 1.6 and 1.7 focbox?
is there an official reference? I haven’t found anything even casual in my searching yet. except maybe 1.7 is immune to the can bus burn out issue and 1.6 isn’t?
can I reuse the focbox 1.7 bottom case and thermal pad with a 1.6 replacement?
the thermal pad has burn marks on it. so … idk if I can clean that. apply some kind of thermal paste again? idk.
it’s a bunch more work to remove the aluminum plate and therefore all the electronics (see pics above). in order to get to the bolts holding the focbox bottom case in place.
trying to decide what to do there.
would a swap for a unity be an improvement?
If.i have to remove all the electronics to get the focbox bottom case off the aluminum plate well i can change anythign at that point and it’s my understanding the unity might have better thermal performance.
Why did this happen?
what else should I check before hooking up a replacement so I don’t just blow the replacement?
is this focbox repairable?
is this the type of thing people have repaired or is this thing junk?
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looks like focbox 1.6 will fit fine. in the same 1.7 case. I just need to learn how to deal with / replace the thermal pad and “properly” install it in the new base.
The internet seems to suggest you should never reuse a thermal pad.
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some ones been down this path before. and improved some things?
Generally you dont want to reuse a conformal materiallike thermal pads because its been formed once it often wont reform or make contact the same way again.
– https://www.reddit.com/r/buildapc/comments/bo5gin/reusing_thermal_pads/
someone saying don’t reuse a bit less firmly and with a reason.
my Jedbox thermal pads came out without marks, intentions, or any indication of use at the FETS
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Ok,
My plan now is:
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take apart motor and look for any signs of shorts. perhaps learn more tests. because it seems ok.
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replace the 1.7 blown focbox with a 1.6 I have on hand. rolling with the 1.7 on the other side. not blocking on understanding the differences better.
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the replacement 1.6 will go in the existing 1.7 base case. so I don’t have to take all the electronics out. I will reuse the nice thermal pad from the 1.6 which is nice and clean. I will transfer it with tweasers.
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I’ll watch thermals. for variance between the two.
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I’ll order some 8W/mk 2mm thick thermal pads and when they come swap it out.
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observe thermals see if there’s any difference.
after that… if you see any observable differences in temp. maybe try a .75-.8mm copper shim on the heatsink use artic silver or the like to afix it… from my studying, thicker thermal pads are way less efficient at heat transfer… I just made the heat sink come up and match the 1mm thick thermal pads effectively squishing the thin thermal pad properly…
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gonna be harder than easy.
I loctite 680’d my bearings to the shaft to prevent reoccurance of motor shaft wear
now I’m paying that price. 
heat got me some of the way there.
just bitchin’ for the moment. will keep trying.
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bearing stuck on the shaft from the other end of the bell.
for now I’ve installed a replacement motor. till i figure outif I can deal with the bearings.
inspecting the removed motor I don’t really see any signs of short.
also don’t seem to have shot all the pictures I thought I did.
TLDR status: Board is together with focbox 1.6 transplanted and a new motor. still inspecting old motor to see if cause lies within.
Not sure I ruled out the motor. but I didn’t find anything obvious. so I still don’t know why it happened. or if it’ll happen again.
Got an inductance meter. following a suggestion from @kook
I think I figured out how to calibrate it and use it.
then I went to find the docs and… they’re not too much more help.
measuring between any two phase wires they all show about 51µH saved vesc configs said inductance was 11.18µH not sure what to think there.
Wanted to check the resistance of each phase, but it turns out my multimeter doesn’t really go that low. it will display down to 1/10th an Ohm. and it measured each pair of phase wires at 0.2Ω
could do some trickery with a voltage divider
so nothing obviously wrong? or maybe better tests on the motor required? not really sure.
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