XR board with dead MCU?
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@lia Thanks. The whole harness Ohms out OK.
Maybe this is a BMS issue after all; when I press the power button on battery only the voltage never gets to the power connector going toward the main board._MK
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Q15 seems suspect. Ohming out base, junction and collector I’m measuring open circuit between two pins.
I’m coming up dry on the PN of the transistor. Not sure if Q15 could explain the behavior.
Also; the board came up on the app this time.
Battery shows 1% SoC even though voltage is 61.5V.My suspicion has moved to BMS.
_MK
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@mk_ A smiliar issue like yours happened when I got water in my battery box. I would check for water in your battery box, or check the health of your BMS/Battery
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@loaffette thanks. I don’t visually see any damage aside from a discoloration around Q15. That in itself doesn’t seem like a smoking gun. Ohming it out makes me think Q15 is damaged.
Do you have any info on recommendations for verifying the BMS health?
_MK
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@mk_ for me, I found that letting the BMS and battery dry out, wiping them down of any water, along with the internals of the battery box helped. I'm not an expert in electronics repair, but within a couple hours I had a working board
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I took some iso to a pair to check. Q15 on the BMS appears to be marked with 1A with either a J or 4 marked sideways. I didn't find much for 1AJ but did for 1A4. Both appears to be a SOT-23 package.
BMS 1
BMS 2
A little googling claims this is an NPN medium power transistor. Here's a selection: https://www.s-manuals.com/smd/1a
This one is specifically for 1A4.
https://www.s-manuals.com/pdf/datasheet/z/x/zxtn25040dfh_zetex.pdf -
@lia Thank you! This helps. I'll get some of these from DigiKey and see how far that gets me.
In the interim, I poked around the BMS some more.
When I connect power to the battery connector (external supply plugged into battery connector) and trigger the power button I briefly get a 5V coming out of the power supply but it shuts off after only a few seconds.Q2 (large FET on the battery side) Ohms out OK (high impedance between pins), but I get no output on the Source pin when triggering power on. (I read the input power on the Drain pin (the fat pad of the transistor) but the transistor doesn't get turned on when power button is applied to get the power to the rest of the board.
Q12 (large FET on the controller side) appears dead; measuring a source to drain short circuit there.
Any thoughts from the community appreciated as to where to poke around next.
Cheers._MK
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Thanks for your help, everyone, my board is back up and running.
I swapped out Q15 and Q12, both of which Ohmed out broken.What's interesting to note was that when I first assembled the board I got a warning that my battery is dead (below 10%) and it was showing 1% on the app so I figured there is more to do. I then plugged it into a charger to see what happens and within a minute the battery went to 99% and I went for a ride. Pretty stoked.
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@mk_ Congrats on the repair!
Regarding the battery percentage that sounds typical for a BMS like this. I wouldn't worry about that, just the gas gauge reading needed resetting via a charge cycle :)
Float on ^-^
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@mk_ great work. Will investigate if I have same problem. Did you buy the transistors Lia suggested or which kind did you replace them with?
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@kallepetter Sorry for a late reply.
I ended up going with a higher voltage rated replacement for Q15:
https://www.mouser.com/ProductDetail/522-ZXTN19100CFFTAThis is the stock one:
https://www.mouser.com/ProductDetail/621-ZXTN25040DFHTAFor Q12, I got these:
https://www.mouser.com/ProductDetail/595-CSD19536KTT
