Our Electron is powered via a 12V AC transformer through a bridge rectifier and capacitor smoothing.
The battery is plugged in and isn’t needed for general usage.
After a number of weeks we had a failure in the electron and the cause of that appears that C5 has shorted out. The resistance is extremely low. With C5 in, the particle doesn’t boot. When it is out, it appears to work.
What could cause C5 to fail?
This caused the transformer to fail so we do need to know why it failed if possible.
Is it C5 or C4?
The reason why i asked is that I don’t see the pin PMID (where C5) is attached being used (i might have missed it)
C5 rating is: Ceramic Capacitor, X5R, Low ESR (<70 mΩ) 22uF 6.3V (if the BOM is accurate)
Also, you need to measure the impedance of the C5 when it’s removed from the circuit to know if it’s really shorted.
Fairly sure it it C5. It is connected to the PMID Pin of the bq24195 IC (Pin 23).
I took it out and measured it again and is it measuring 0 Ohms, 2.69nF. There is a bit of what I might class as ‘visible damage’.
This isn’t a part I would expect to fail.
Looking through all the info I can, the max input voltage is 17V (This is lower than I thought). It is reasonable that a small power spike could have propagated through the device. Based on the construction of the BQ24195, if the Q1 gate was open and the spike came through, this could cause the capacitor to over volt (At 6.3V, it is pretty wimpy in that regard).
I can’t prove any of this though which is what I would like.