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Fubarino SD, High Voltage on Vout #24

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JacobChrist opened this issue Apr 14, 2019 · 2 comments
Open

Fubarino SD, High Voltage on Vout #24

JacobChrist opened this issue Apr 14, 2019 · 2 comments

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@JacobChrist
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So a common failure mode of the Fubarino SD and Mini is when students short 3.3V to GND (for too long). This causes the regulator to go and the board to stop working. So I sat down today to try and repair some five blown boards and found that the when powered with USB that Vout will have between 14-25VDC on it. The 3.3V output will also have a large voltage and this has probably fried the processors too. I suspect that the failed regulator, D1 and C3 are working together to form some kind of charge pump. Very strange.
@JacobChrist
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I removed the microcontroller and replaced the regulator. With the microprocessor off the board, 5V on Vin. I get 28V on Vout and 3.3V. Weird. If I press either button (to add a little load) the voltage drops a couple of volts but still well above 20VDC.

@JacobChrist
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Your gonna laugh. My probe was on x1 and my scope on x10. I'm shelving this problem for the moment.

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@JacobChrist