BQ24780S: System don't charge the batterie

Hi Thomas,

Pin 3  (CMSRC): 19.34v
Pin 4  (ACDRV): 19.38v

This the values of these two pins may be why you have an issue.  I would need to see the motherboard schematic to know for sure, but generally ACDRV is attached to an N-channel MOSFET that is used to block the adapter from the system.  In order to turn the pass FET on, ACDRV is driven 6V above CMSRC.  With the measurements you are showing now, that FET will be off.  In this state the motherboard is running purely off the battery and the adapter is cut off from the system.

The condition to turn the FET on is that ACDET (pin 6) is above 2.4V.  You show it as 0V.  Usually this is a simple resistor divider that divides down the adapter voltage, so if you are reading 0V, then maybe one of the resistors in the divider got damaged, although that would be a rare occurrence.  Again, it is difficult to know the possible cause without seeing the schematic.  But these measurements are consistent with your description that it doesn't charge even though the adapter is plugged in.

Regards,

Steve

Hi Steve,

First, thank you for your great help :)

I am attaching the two documents I have (a PDF and a .FZ for boardview) to this answer.

I lack knowledge in electronics but I'll do my best to understand :)

Edit : after further testing, Pin 6 is at 2.6V

Edit 2 : I've checked again and I may have a lead, on the charger, I've got this schematic:
 
I was able to identify the items directly connected to ACDRV and CMSRC.
The PC8901 (blue) and PR8910 (red) components have been removed and replaced by a single wire because they were damaged... can this be the cause? (PR8910 = 4.7 Mhom resistor and PC8901 a capacitor)...

Edit 3 :  if I put Pin 3 at 0v (cut it off), can that solve my problem? (even if it's not clean)...

Best regards,

Thomas C.

ASUS UX305CA RG.pdffixbios.com_UX305CA.zip

Hi Thomas,

I think that the diagram that you show above corresponds to the soft-start circuit here on our EVM:

Then based on the connections in your diagram, I think PC8920 = C13, PR8910 = R7 and PC8901 = C12. 

Ideally, if one or more of the components was damaged, you would replace them with like components.   I am not sure what replacing with wires is going to do, but I can tell you that the capacitor needs to be left open circuit and only the resistor wired over if that is how you are going to try and repair it. 

You said that the capacitor and resistor were both removed and replaced with a single wire because they were damaged.  If this is the case, the wire needs to only connect the two pads of the resistor.  You should see both pads of the capacitor open.  If you short over either C12 or C13, it would prevent ACDRV from turning on the FETs because it would be shorted to CMSRC.  This seems to be the issue you are reporting, so I would definitely say to double check that whichever capacitor was removed, you haven't shorted over that capacitor with the wire.

Also, I just need to point out that replacing these components with a wire is not a configuration that is supported by TI.  I can give you advice to help you debug what you are seeing, but I am not recommending that you repair the board in this way.  These components should be replaced by new components to repair the board properly.