Asus Q551L Not Charging

[mgrharry]

Working on an Asus Q551L. The DC jack center pin had broken loose from the socket, and the only way to charge it was to push and hold the charger in. I repaired the center pin and reflowed the other pins as well. Meter now reads a steady 19v on center pin and ground pins have continuity. But the system does not detect the charger. It will power on from the battery which still has partial charge.

Where to start troubleshooting next?

Photos are attached.

[mgrharry]

Re: Asus Q551L Not Charging

Maybe there's a blown resistor?

[mon2]

Re: Asus Q551L Not Charging

Locate and share the topside markings of the battery charger IC. Follow the dc connector and you should see 2*DCin mosfets. These mosfets act like solid state switches. We need to know the charger IC so we can compare the details with other reference designs to learn about your board.

It is possible that your charger IC will be the common 'BQ' type from Texas Instruments.

This charger IC will have an ACDET pin that is used to detect the presence of the adapter. Often, a resistor based voltage divider.

[mgrharry]

Re: Asus Q551L Not Charging

TPS51362
https://pdf1.alldatasheet.com/datash.../TPS51362.html

Pics attached

[SMDFlea]

Re: Asus Q551L Not Charging

TPS51362
https://pdf1.alldatasheet.com/datash.../TPS51362.html

Pics attached

Q551LN Boardview https://www.badcaps.net/forum/showthread.php?p=1199602

[mon2]

Re: Asus Q551L Not Charging

See attached. If your board layout is similar, we need to know the markings of this IC = charger IC.

[mgrharry]

Re: Asus Q551L Not Charging

Ahh, there it is, thank you! It's BQ735.

[mon2]

Re: Asus Q551L Not Charging

Good stuff. Measure the voltage to ground of pin #4 of the charger IC = ACDRV. Do so with care. Ok to measure at the 4k resistor that is on the same pin.

[mgrharry]

Re: Asus Q551L Not Charging

Measured pin 4: 0v nada

[mon2]

Re: Asus Q551L Not Charging

Locate and remove the 4k resistor on this ACDRV pin. Do not lose the resistor.

Power up and test again the voltage to ground of ACDRV pin.

[mgrharry]

Re: Asus Q551L Not Charging

voltage with resistor removed is .06

[mon2]

Re: Asus Q551L Not Charging

Check voltage to ground of REGN pin #16. Also VCC at pin #20 on the charger IC. This ic is powered through pin #20.

[mgrharry]

Re: Asus Q551L Not Charging

pin 16 = 6.11v
pin 20 = 19v

these are with the resistor for ACDRV removed.

[mgrharry]

Re: Asus Q551L Not Charging

One other odd thing-- if it's sitting plugged in for a long period of time, 1hr plus, the system will power on and the fan will run. It's only happened with the bare board connected to power so I don't know if it's posting but seems worth mentioning.

[mon2]

Re: Asus Q551L Not Charging

With the ACDRV resistor removed, what is the voltage on the ACDRV pin on the charger IC? Measure with the adapter connected.

[mgrharry]

Re: Asus Q551L Not Charging

Hmm, pin 4 is cycling between 0 and .38v

Just to be sure that I removed the correct resistor, I've attached a photo. The area where the removed resistor was is marked in red.

[mon2]

Re: Asus Q551L Not Charging

No. Place the removed resistor back onto the board.

Review posts #5 and #6 of this thread.

The boardview will offer the correct location for the 4k resistor being referenced.

The yellow highlighted pins are the gate pins of the DCin mosfets.

Using the boardview file, mouse click on the ACDRV pin #4 of the charger IC. The software will highlight all connected pins to the selected one.

Now, review the backside of the board to locate the DCin mosfets and the highlighted 4k resistor will be visible.

Select the other side of the resistor and pin #4 of the mosfets will be highlighted.

This is the 4k series resistor to remove so we can confirm the gate voltage drive is ~25v (adapter voltage+REGN voltage=~25v).

[mgrharry]

Re: Asus Q551L Not Charging

Ahh, shit, sorry about that. I missed your second board view screenshot where you pointed out the dc in mosfets and the resistor. I'm an idiot.

However, we can mark this as a case closed-- I replaced PR8813, CHG_ACOK, resistor from a donor board, and was ready to proceed with retesting and then removing the CHG_ACDRV resistor but I figured I'd just double check the system and it is now charging correctly. Did a few charge up / down and power cycles and it's working fine.

I did make a side by side image of the board view and actual board with the CHG_ACDRV resistor circled in red. I'll go ahead and post it in case it can help someone else in the future.

Thanks for all the tips.