ASUS TUF Dash Motherboard FX516 REV 6.0 Model Device Not Charging

[lazenes]

Remove all power. Measure the resistance across PR8913. Is the resistance close to the schematic value? If yes, measure the resistance to ground of the point with 0R ohms. Either the PR8913 resistance is too high or there is a short on this line. From the board view diagram, there should be a voltage here.

I've removed all power and measured the resistance across PR8913. I'm getting around 60k ohms, but the schematic shows it should be 120k ohms.

It seems the resistance is not close to the schematic value, being roughly half. Does this suggest the resistor itself is faulty, or could it still indicate a short on the line?

[mon2]

This measurement may be off due to the fact that the resistor is in-circuit as compared to being removed and on your work bench. On your work bench, the measurement will be more accurate.

However, at 60k ohms, you should still have a voltage on pin #21 (ILIM) unless this pin is being shorted to ground.

Remove all power. Measure the resistance to ground of pin #21 (ILIM). We are now checking if the resistor @ PR8914 is shorted or not. What is the resistance in ohms?

Based on the shared information, if PR8914 is not shorted, then there should be a voltage on pin #21 (ILIM) to define the peak charge current for the battery.

[lazenes]

This measurement may be off due to the fact that the resistor is in-circuit as compared to being removed and on your work bench. On your work bench, the measurement will be more accurate.

However, at 60k ohms, you should still have a voltage on pin #21 (ILIM) unless this pin is being shorted to ground.

Remove all power. Measure the resistance to ground of pin #21 (ILIM). We are now checking if the resistor @ PR8914 is shorted or not. What is the resistance in ohms?

Based on the shared information, if PR8914 is not shorted, then there should be a voltage on pin #21 (ILIM) to define the peak charge current for the battery.

I measured the resistance between PR8914 and ground, and it is about 87 ohms

[mon2]

Ok. That explains it. Flux and remove PR8914 off the board. Do not lose the part. Then allow it to cool and measure it again. Is this part still ~87R ohms?

Assuming yes, hunt for any part you may have that is close to the schematic value of 68K ohms. This value is not critical. Even leaving the resistor off should be ok but then we are applying ~3v onto this ILIM setting and requesting the charger IC to use a high current to charge the battery. I think it will be safe to do so for initial testing but long term solution is stuff a valid resistor @ PR8914.

[lazenes]

Ok. That explains it. Flux and remove PR8914 off the board. Do not lose the part. Then allow it to cool and measure it again. Is this part still ~87R ohms?

Assuming yes, hunt for any part you may have that is close to the schematic value of 68K ohms. This value is not critical. Even leaving the resistor off should be ok but then we are applying ~3v onto this ILIM setting and requesting the charger IC to use a high current to charge the battery. I think it will be safe to do so for initial testing but long term solution is stuff a valid resistor @ PR8914.

I removed PR8914 and measured it out of circuit. The value is 67.9kΩ, so it seems normal. Should I try powering the board with the adapter while the resistor is removed?

[mon2]

Measure the resistance to ground of the ILIM pin (without the PR8914 resistor). Suspecting that you will still have a low resistance to ground on this pin.

[lazenes]

Measure the resistance to ground of the ILIM pin (without the PR8914 resistor). Suspecting that you will still have a low resistance to ground on this pin.

~87R ohms
When I measure PR8914 out of circuit, it reads about 68kΩ. But when I solder it back on the board, the resistance drops to around 87Ω. What does this mean?

[mon2]

Leave PR8914 off the board. Then measure the resistance to ground again at pin #21 (ILIM). What is the resistance without PR8914 soldered on the board?

[lazenes]

Leave PR8914 off the board. Then measure the resistance to ground again at pin #21 (ILIM). What is the resistance without PR8914 soldered on the board?

With PR8914 removed from the board, I measured the resistance to ground at pin #21 (ILIM) and it reads about 101Ω.

[mon2]

Check if you have a capacitor @ PC8911 on your board. If yes, flux and remove it. This capacitor may be shorted. Then measure the resistance again at this pin to ground.

[lazenes]

Check if you have a capacitor @ PC8911 on your board. If yes, flux and remove it. This capacitor may be shorted. Then measure the resistance again at this pin to ground.

"I removed PC8911, but nothing changed. The resistance to ground at pin #21 (ILIM) is still the same."

[mon2]

Any liquid damage to PU8900? Has this part been replaced in the past? This resistance is too low on this pin. If no liquid damage then this charger IC may be defective.

You can also confirm the same by testing diode mode. Remove all power. Meter in diode mode. Red meter lead to ground. Black meter lead onto this same ILIM pin.

What is the measurement?

[lazenes]

Any liquid damage to PU8900? Has this part been replaced in the past? This resistance is too low on this pin. If no liquid damage then this charger IC may be defective.

You can also confirm the same by testing diode mode. Remove all power. Meter in diode mode. Red meter lead to ground. Black meter lead onto this same ILIM pin.

What is the measurement?

I am measuring 108 ohms in diode mode.

The integrated circuit hasn't changed. I took it out and put it back in.

I guess I should order a new PU8900 integrated circuit and try it out.

[mon2]

In diode mode, the units of measurement will be in volts. Double check if you are in diode mode. To confirm, touch your meter probes together and you should hear a tone beep.

[lazenes]

In diode mode, the units of measurement will be in volts. Double check if you are in diode mode. To confirm, touch your meter probes together and you should hear a tone beep.

I guess I should order a new PU8900 integrated circuit and try it out..

0.094v

[mon2]

Yes, I would agree. Order a spare as they are not too expensive. The diode measurement is showing this line as being shorted.