[SOLVED] Red light flashes next to barrel-port

[Carl]

OP updated

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My PBP isn’t charging the battery at all, unlike Carl’s which seems to be trickle charging, so our faults might be slightly different. Anyway, I took a look at the resources available.

From the schematic (page 11) you can see the LED next to the power socket is connected to the 'STAT' pin of the BQ24171 battery charger IC.



From the BQ24171 Datasheet:

"Open-drain charge status pin with 10-kΩ pullup to power rail. The STAT pin can be used to drive LED or communicate with the host processor.It indicates various charger operations: LOW when charge in progress. HIGH when charge is complete or in SLEEP mode. Blinking at 0.5 Hz when fault occurs, including charge suspend,input overvoltage, timer fault and battery absent."

My interpretation (the interpretation of a novice) of the fault conditions are:

Charge Suspend - Disables battery charging when the temperature of the battery pack is below 0 °C or above 60 °C 
Input overvoltage - If (my math is correct and) the input increases over 6.5v or drops below 2v charging will terminate. 
Timer fault - If the battery voltage is too high or low it won't be charged. I can't quite get my head around how to work out the values that trigger this, I’m sure someone with experience could work it out easily. 
Battery absent - There’s a little dance here where the BQ24171 applies a discharge current and then monitors the voltage to determine if a battery is present. I won’t pretend to understand anymore than that.

When I realised that my PBP wasn’t charging I removed the battery and charged it using an external charger (TP4056). The battery charged without issue and it was cool to the touch, although it was only slow charging which took about 10 hours to go from 3v to 4v. The point being the cells themselves seem to be fine. However, I haven’t been able to test the thermistor, if that’s faulty it could cause a ‘charge suspend’ condition. Additionally, with the battery charged to 4v it’s in the accepted voltage range and should not cause a ‘timer fault’.

I’ve used a number of different charging sources (different USB wall plugs, the provided barrel plug adapter) but all have been 5v, give or take 10%, which means they shouldn’t be causing an ‘overvoltage’ fault.

At the moment I’m hoping this is a bad thermistor, that would be the easiest fix. If it’s a board-level component then I don’t think I’ve got the skills or tools to be able to find the bad part.

I hope that information is useful to anyone else having this problem. Happy to try any other tests that might narrow this fault down. 

Cheers,
Ron

Hi Ron,

Thank you for the insightful information. Have you managed to make any progress?
Our symptoms sound similar since my PBP also completely stopped charging from the barrel-port - however I managed to solve all my symptoms by using a USB-C power supply (updated OP). For some reason the power supply that came with the PBP and or barrel-port appeared to be damaged/faulty for me. Have you tried charging using the USB-C port?

Kind regards,
Carl