If you don’t have the proper tools then sure, that’s the safer approach.
The reverse-polarity battery fried my laptop’s USB port when I tried to charge it via the DSO so I’m not feeling as generous as I might otherwise have been. 
It seems my battery is still charging normal after I swap the red&black battery wires in the JST plug.
After leaving the quad off with USB cable plugged in for all night, the battery voltage is measured at 4.3v 
(with a Fluke 179 - should be max at 4.2 only)
However, even with this voltage, the quad still reports that my battery is empty (red empty battery symbol).
Even after all night, the red light is still on.
Anyone has any idea how to fix this, please?
Thanks very much
-Thanh
My only suggestion would be to measure the Vbat signal (between U14 and U15 on the schematic) and see if that is 1/2 the actual battery voltage. If not, then this voltage divider circuit is defective, or more likely, the reverse voltage damaged that input-pin on the STM.
If the STM can’t see the battery voltage, then it will pull down the CHRG output signal and this could possibly force an overcharge condition to the battery and also keep the red LED on.
Does the red LED turn to yel/org when the unit goes to sleep?
I haven’t had a chance to make the board-level fix, but since I’ve already tried charging it in the reversed state it’s sounding like I shouldn’t bother with the battery at all.
I’m leaning toward Minty Boost power via USB. Much safer than an overcharged LiPoly pack!
Thanks for your help.
The STM chip does see the voltage changes. When plugged into the USB port, the charge indicator goes green.
I measured the voltage at R51&R52 bridge, it’s exactly half of the input voltage. In my case, with battery voltage at 3.9v, I measured only 2.6v on top of the R52, thus it’s only 1.3v at the Vbat point. So the STM thinks battery is low for obvious reason.
The voltage at the on/off switch is only 2.6v. The voltage of the battery is 3.9v. So something is lost in between.
Looking at the schematic, I don’t understand why there is an X betwen pin 3 of U19 and the switch? Does that mean pin 3 is not connected?
If pin 3 is not connected then the voltage is passed from the battery solely through the diode inside U19. Is it a Schottky diode or is it a zener diode? I think it should be a Schottky diode. So maybe U19 is dead in my board. If I make a jumper between the switch and the battery, the quad indicates it’s 50% charged.
Could anyone please measure the voltage at the middle pin of your quad’s switch?
Thanks very much
-Thanh
My situation is the same. But I notice:
-
When QUAD is powered from the “strong” USB port battery meter shows ~4.5V, battery indicator is full and real voltage on battery is 4.08V.
-
When powered only from battery, battery meter shows 2.85V, scope goes OK, real battery voltage is STEEL 4.08V, battery indicator is empty. So, the battery is OK and fully charged.
-
When QUAD is powered from the “weak” USB port(e.g. hub), battery meter shows ~3V and battery indicator is NOT empty.
Conclusion:
STM measures NOT battery voltage, but something else. May be hardware or software bug.
Concerning the X on pin 3 of U19, my assumpion is that U14 has some king of backfeed inside, which allows battery voltage feed throgh the diod in U19 when not powered from USB.
PS Yes and it is! It measures powerline not battery. In the righ way the divider R51-52 must be connected to point VB but not to the 3V6 which depends on the power status.
And of coarse wrong calibration of the ADC on the PC2_AIN12.
BTW, there is not any cut from U19 pin3 on board.
Just for the record, I “fixed” mine by trimming back the plastic shroud around the battery socket so I could plug it in backwards.
I think the charging circuit’s dead, but I have external LiPoly chargers I can use for topping it up.