Posts made by MK_

Another board, another repair. Starting with a dead board, don't know full story. BMS def fried, started off with checking FETs, Ohmed out caps for shorts, etc.; found Q1 and Q13 to be blown. I replaced them and for a good measure replaced Q15 as it's cheap and easy. Board went from dead to coming alive but just for a few seconds before shutting off.

When the power button is pressed, the board comes up, the blue light on the power button starts blinking and after a blink or two it shuts off. Any suggestions where to start looking next?

(I found some reference in other threads that the current sense could be the cause so replaced the chip with no improvement, haven't touched the resistor, that seems OK).

@kallepetter Sorry for a late reply.
I ended up going with a higher voltage rated replacement for Q15:
https://www.mouser.com/ProductDetail/522-ZXTN19100CFFTA

This is the stock one:
https://www.mouser.com/ProductDetail/621-ZXTN25040DFHTA

For Q12, I got these:
https://www.mouser.com/ProductDetail/595-CSD19536KTT

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.

@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

@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

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

@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

I have a XR board which has the following symptoms:

• It doesn't turn on at the press of a button

• When charger is connected, it appears to charge fine (light turns red on the charger)

• When charger is connected, app sees the board, which seems to mean the bluetooth module is fine, however, it is unable to fully connect to the board (stuck on activating...)

I have taken the board apart and the battery does appear charged, BMS looks good.

Main board also looks good visually, I haven't yet starting probing voltages. (I'm a EE so fairly comfortable with this)

Question to the forum, have you guys come across these symptoms?
My initial though is the main micro is not coming up. Could be something with the power rail (I don't know at this point if the BLE module is on the same rail as the MCU).

Thanks for any info as it will invariably shortcut my troubleshooting steps.

Cheers.

_MK