S2 Reverse TFT - I used wrong Battery Polarity😒

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tyeth
 
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S2 Reverse TFT - I used wrong Battery Polarity😒

Post by tyeth »

Hi, I was aware of polarity and had tested successfully, then added a 5v usb-c solar panel, then tried without battery, amazing it worked in british sunshine. I then disconnected solar too.
Then I reinserted battery backwards by mistake and smelt the electric smoke smell. Looked like the board was dead, and now twenty minutes later it does get neopixel power when run from usb-c, but the screen doesn't turn on. Not sure what to test/replace... Similar to this issue which seemed to suggest the board naturally recovered except lipo charger, but maybe I got the wrong end of the stick.

viewtopic.php?p=953395&hilit=polarity#p953395

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tyeth
 
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Re: S2 Reverse TFT - I used wrong Battery Polarity😒

Post by tyeth »

This conversation / issue is also being commented on in discord. (adafru.it/discord) in the help-with-hw-design channel. https://discord.com/channels/3272547085 ... 4317832204

Nothing really concluded, except a few things to check:
discord conversation showing LDO and mosfet to check
discord conversation showing LDO and mosfet to check
Screenshot 2023-03-02 142011.png (312.7 KiB) Viewed 86 times

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tyeth
 
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Re: S2 Reverse TFT - I used wrong Battery Polarity😒

Post by tyeth »

So having probed it a bit, I think the diode is unhappy, but to be fair it could be anything (no obvious shorts).
Curiously the white-neopixel is shown before the display is initialised in the factory sketch, but it never progresses, when on USB-C.
I then tried battery and it runs normally!
Adding usb-c is fine and it keeps running (started on battery).
Having just usb-c doesn't work (only white neopixel), and adding the battery while usb is connected causes no change, but resetting the board it boots normally.

This suggests to me it's the battery fuel guage chip, or charging chip, or diode. The mosfets looked alright with multimeter.

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tyeth
 
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Re: S2 Reverse TFT - I used wrong Battery Polarity😒

Post by tyeth »

Looks like I took out the Orange charge LED, the shottky is looking iffy, and the MAX17408 is unresponsive without a battery attached, chip not detected, but then reads fine after first zero value read when a battery is attached.
Sketch to test battery chip results in Serial doesn't behave properly without battery initially attached. If I boot from battery or reboot once with battery attached, I can then remove the battery (causes max value returned by IC) and then reboot board and serial replies from the sketch work with just usb attached and the sketch runs and reports no max chip, but if battery attached then chip responds. The serial works fine every time with battery attached based booting (or a reboot once attached battery), but not if only ever usb powered. Normal flashing works fine without battery attached and booted from usb power.

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adafruit_support_mike
 
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Re: S2 Reverse TFT - I used wrong Battery Polarity😒

Post by adafruit_support_mike »

Conneting a LiPo with the wrong polarity forward biases polarity protection diodes in the ICs.. potentially all of them. Chips directly connected to the LiPo like the charger, voltage regulator, and fuel gauge are more likely to be damaged than ones whose electrical connections are more remote.

I wouldn't expect any damage to LEDs or diodes. Those will be reverse biased by a LiPo with the wrong polarity.

You may need to lift components off the PCB one by one to get clear information about where the damage is.

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tyeth
 
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Re: S2 Reverse TFT - I used wrong Battery Polarity😒

Post by tyeth »

adafruit_support_mike wrote: Fri Mar 03, 2023 11:03 pm I wouldn't expect any damage to LEDs or diodes. Those will be reverse biased by a LiPo with the wrong polarity.
I tested the LEDs with multimeter, and the orange charge LED wont light (red LED does light with multimeter, plus orange does on another board), but the lipo charger appears to be tranfering charge / presenting voltage to the battery pin. I think I'm needing to replace that charge LED too, but will know more after the lipo fuel guage IC is replaced. Shame it's so fiddly to get a current measurement on the battery, but might have to rather than lift and replace the lipo charger (got a spare but not an SMD soldering pro)

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tyeth
 
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Re: S2 Reverse TFT - I used wrong Battery Polarity😒

Post by tyeth »

Having asked for a bit of advice on Ask an engineer, was advised to not attempt the repair if the feather still works at all as the risk of damage is huge.

The device does work over USB if a battery is left attached, but wont boot without the battery, and the fuel guage chips dead but that is still a reasonably working device (screen etc) so I will not be rushing to repair it.
I do want to attempt adding BMP280 to one of the feathers, and improve my SMD soldering so maybe I'll practise on this one.

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