ASUS GA401QM No ACDRV, No CMSRC

[ResoluteHawk]

I have an Asus G14 (GA401QM) that has a power issue. Originally the board had a shorted 5V rail and dead EC. I reballed a working EC, soldered it on, and I resolved the 5V issue by replacing the APL6012 and the low side 5V mosfet. Resistances on all power rails are healthy now, but 20V does not make it through the first MOSFET. 20V is present on the drain of the first MOSFET, but there is no voltage on the gate or source.

When diagnosing this issue, I thought that the issue was due to the BQ24800 chip not outputting the correct signals so I soldered on a known working chip and the same issue is present. To check whether the chip that was originally on my board is good or not, I soldered it on to the working board and it works fine.

Resistances and voltage measurements are attached in the Word document and boardview/schematic are in the respective section on this forum.

[mon2]

Replace PQ8901

[ResoluteHawk]

Just tried replacing it with the exact same mosfet from a working board. Same result. Still 4V at the current sense resistor, 20V at the drain of the first mosfet, and 0V at the source.

[mon2]

The current sense resistor across ACN / ACP pins of the charger IC do not appear to be soldered correctly. Confirm this detail. The charger IC may need a reflow as well. You should have the same voltage on each side of this current sense resistor. Also the same resistance to ground on each leg of this important resistor.

[ResoluteHawk]

Pins on the BQ chip are soldered perfectly, and the pins make contact with the board. Same resistance to ground is present on both sides of PRS8901, but not on the BQ chip. BQ chip presently on the board is confirmed working correctly on another board.

[mon2]

You will need to flux the BQ pads and allow for the BQ chip to melt into place once the solder is in liquid form. This is highly recommended for a good contact.

[ResoluteHawk]

Also, I should have mentioned that after I restored the 5V rail to normal resistance, I also had to take PC9301 off the board as it was a blown capacitor dragging the battery charge rail down to ground. Resistance after removing that cap is back to normal.

I'm wondering if the cause of this no power issue is somewhere in the protection circuit.

[ResoluteHawk]

Couldn't have soldered those pins any better.



Same readings still.

[mon2]

With no power -> measure the resistance between pins 1 & 2 directly on this charger IC. We are checking the full current loop path for the main power rail. What is the measurement?

[ResoluteHawk]

Resistance between pins 1 and 2 of the BQ chip rises north of 3M Ohms. It should be continuous as measured on a working machine.

Might be looking for a blown 0 Ohm resistor somewhere.

Also, new discovery: Laptop turns on and POSTs into the BIOS with just a battery.

[mon2]

You have a trace break in this current sense path. Use the same method to trace from the ACP to one side of the current sense resistor, etc. Hunt it down in segments and repair where the trace or path is broken.

[ResoluteHawk]

I'm also going to add that the orange charge light (middle LED) comes on when just the battery is connected and the laptop is powered off.

There should be no charge light since no charger is connected.

You have a trace break in this current sense path. Use the same method to trace from the ACP to one side of the current sense resistor, etc. Hunt it down in segments and repair where the trace or path is broken.

I found another post on this forum from someone who said they had 4V on the main power rail with just the charging cable plugged in (just like my problem).

They fixed it by checking the dual diodes that supply power to the BQ chip. On this board, that would be PD9003 and PD9004. I don't see how those diodes would be relevant though since 19.85V is present on VCC of the BQ chip.

[mcplslg123]

Either the CLR is burnt or there is connectivity issue between ACN/ACP pins to CLR.

[ResoluteHawk]

Either the CLR is burnt or there is connectivity issue between ACN/ACP pins to CLR.

What do you mean by the CLR?

[mon2]

Post # 11

[ResoluteHawk]

Post #11 doesn't mention anything about what CLR is. I have no idea what he is referring to.

Also, I checked the two diodes that supply the power to the BQ chip, and both of those diodes have a 0.3 voltage drop from one end to the other.

Current sense resistor one end to the other end => Continuous tone.
ACP at BQ chip to the current sense resistor => Continuous tone.
ACN at BQ chip to the current sense resistor => 0.8 voltage drop < something wrong here
Connection between ACN and ACP directly on the BQ chip pins => Above 3M Ohms
VCC (Pin 28 of BQ) = 19.85V when AC is plugged in.

I'm lost. I don't know where else to look and I don't see any other path from the BQ chip to the current sense resistor than what I already tested.

Are we suggesting that the trace itself that is in the layers of the board is damaged?

[mon2]

ACN at BQ chip to the current sense resistor => 0.8 voltage drop < something wrong here
Connection between ACN and ACP directly on the BQ chip pins => Above 3M Ohms

CLR = current load resistor / sense resistor - many ways to say the same thing.

[ResoluteHawk]

Ok that makes sense.

I suppose I could just run a wire from ACN on the capacitor connecting to Pin #1 on the BQ chip directly to the current sensor and see what happens. That's what the trace is doing internally anyway; it would be a dodgy repair but at least the connection would be restored.

[mon2]

Yes - agree on each comment It should work fine.

[ResoluteHawk]

Ok so there's something I really don't understand about how the input circuit works.

I just desoldered the current sense resistor to see what the trace looked like underneath it and see if it was damaged in any way, but I also figured I'd like to see what happens with the voltages if the CLR isn't there. Plugged in power, and now I'm getting 20V at the ACP side and 26V on the MOSFET gates, but 4.3V at the ACN.

Why does removing the current sense resistor yield these results?

What is the purpose of ACP and ACN and why do I still have 4.3V at ACN with the current sensor desoldered?