I know this is an old thread but posting here as the pics posted look the same (whereas many other links will have different version boards).
I had the reverse polarity warning on my display and switched the charging-output-leads round. Why I did this is beyond me as the wiring was correct and I had charged a battery with it the day before...
Now the N-FET AO4468 has released its magic smoke.
Since I have an identical 80W B6 clone, I figured I would use that to:
(1) measure the resistances under/next-to the AO4468, and look at the color-rings to make sure the discoloration in the broken one wouldn't confuse me.
(2) confirm the posted solution to the initial fault (reverse polarity) is indeed correct for my case.
Now I am running into several issues.
- internet is broken. It won't give me a solution what value a black-green-silver-gold-black resistor should be. And I am fairly certain this is what the colors are.
- (1) the resistors from my (at least when last used) working and my broken B6 chargers measure differently and vary from the values found
here. (whole posting
here)
- (2) there is no measurable short (so no PCB trace) between the ground-banana-plug and the ground-of-the-balanceport in my 'working' B6 (a fried PCB trace supposedly causes this "reverse polarity"message, see youtube link below)
The two boards from my 80W B6's are shown below (I have a single 50W B6 too, which is better at e.g. measuring the delta-V of NiMH batteries, the 80W versions don't seem to measure this delta-V at all, but that is a different issue).
Broken B6:
Left resistor reads 45ohm (in circuit, so broken if correct value should be 0.05ohm)
Right resistor reads 0.50 (after subtracting measurementlead resistance and offset, in circuit)
Despite the pic not being perfect, you can see the crater where the magic smoke decided to erupt from on the AO4468.
(When last used) functioning B6:
Left resistor reads 57ohm (in circuit, so broken if correct value should be 0.05ohm)
Right resistor reads infinite (in circuit)
Next I should check if the 'functioning' B6 still functions, because it shouldn't when one of the current sensing resistors (for charging or discharging???) is fried.
Then I think my best bet would be to try to get ONE functioning charger out of the TWO... But I am open for suggestions! (I have a couple of AO4468's, but a 3W(?) 0.05 ohm resistor will be harder to find unless I make it out of resistance wire.)
Reverse polarity fix: