ASUS GA401QM Missing 5v

[ResoluteHawk]

Hello;

I have an ASUS G14 GA401QM that currently has no 5v rail among other things stated below in points #3 and #4. I'd like to see if it's condition can be improved.

1) Originally this laptop had a problem with a shorted main power rail, so measuring at the current sense resistor after the DC IN FETs yielded a very low resistance. Before proceeding further I measured the CPU coils. We get 8.2 Ohms on the farthest right coil (PL8105) and 3.3 Ohms on the four to left left of it (PL8101 through PL8104). When I injected 1v into the current sense resistor, PQH9402 got warm. I removed it and the short disappeared. Replaced it and the short is still gone.

2) Plugging in the power adapter yields no charging light so I disconnect the power. Measuring at the current sense resistor yields a short again. I go back to PQH9402 and measure Pin 1. We're shorted again. I measure PQH9404 and that one is ok. Taking PQH9402 off the board again relieves the short. I have yet to replace it again because clearly something else is wrong.
- PQ9404: Pin #1 in resistance mode measures 3.08 MOhms and in diode mode measures 0.594v drop.
- Where PQH9402 should go: Pin #1 in resistance mode measures 15.55k Ohms and in diode mode measures 0.315v drop.

3) This is where I measured the resistance on the 3.3v and 5v coils. The 3.3v rail at PL8702 measures 3.4k Ohms. Measuring Pin #8 on the BIOS chip in diode mode reads 0.133v drop however reads 595 Ohms in resistance mode, when it should be in the kOhms.

4) The 5v coil at PL8701 measures 12.9 Ohms and the coils for the VRAM right next to it at PL9402 and PL9401 measure 14 Ohms. This is about half of what it should measure.

I don't know where to go next although I have a few pointers to what the issue might be. I suspect it's either a) The EC, b) a VRAM module, c) the GPU itself, or d) A failing PCH.

In any case, it seems like the 5V rail is out with a kill list unless I'm missing something and it's actually another rogue voltage rail.

Schematic and boardview are attached.

[Sephir0th]

Re: ASUS GA401QM Missing 5v

First, it is strongly advised to always change the complete buck converter, so high-side, low-side, controller and driver (if present). That's a unwritten rule.

Then, if the 5V Rail is affected you might deal with multiple defective semiconductors. That's a common outcome when dealing with a shorted +5VALW or +5VS.

However, first suspect should be of course the controller which control the repeatedly blown mosfet (didn't check the schematics so far).

And then we'll see whether there is more.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

I'm not 100% sure of the problem at this point, but it looks like the EC might be the culprit. I'll have to do some more looking around before I take it off.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

If I measure the capacitors around the EC chip, the ones on the EC Power circuit are all shorted to ground (1 Ohm on C3002, C3003, C3004, C3005, C3006, C3007).

C3008 however measures 2.27k Ohms and a 0.317v drop.

Is it safe to say that the EC is screwed at this point?

[Sephir0th]

Re: ASUS GA401QM Missing 5v

My friend, you either ask for assistance and follow the advice or you just do "your thing". Both at the same time does not work, and I can't assist this way.

Buy yeah, the EC could be bad in addition.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

Ok I just removed the EC chip.

Changes:
The capacitors on the EC Power circuit are no longer shorted to ground (they all measure in the K Ohms).
C3008 now measures 0.636v drop and 26.4k Ohms

No changes:
PL8701 is still at 13 ohms.
Coils for GPU memory are still at 15 Ohms.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

BIOS chip on Pin #8 now measures about 1.8k Ohms.

[reformatt]

Re: ASUS GA401QM Missing 5v

It's not normal to have this many faults simultaneously. What is the background of the laptop? Simultaneous issues on multiple power rails are usually the result of something external like a power surge so you may have other issues beyond this.

Could be a big time waster.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

Could be.

The guy said that he was trying to change the RAM and it wouldn't turn on afterward. He went to reinstall the factory RAM and nothing changed.

[reformatt]

Re: ASUS GA401QM Missing 5v

Hard to believe TBH.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

I think I'm just going to call this board a "no fix."

Looks like the short may have gone all the way through to the GPU memory modules and into the GPU (resistance on GPU video memory modules is now 9 Ohms after removing EC).

[reformatt]

Re: ASUS GA401QM Missing 5v

Yeh, multiple faults across different rails, and a dead EC makes you wonder what happened. Especially when a complete dickhead has had his hands in there. Be a no fix from me as there's likely to be more dead pieces of silicon (maybe dead PCH/CPU/GPU).

People like that think nothing of wearing a wedding ring and scraping it across a board with battery connected for example.

[mcplslg123]

Re: ASUS GA401QM Missing 5v

@reformatt the last part of your comments on post#12 is a classic one.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

Ok so I have an update and think I know what happened. I've been working on other laptops and decided to have another crack at this after thinking about it.

My theory:
The previous owner tried reinstalling his RAM but forgot to disconnect the battery before doing so and when he installed the new RAM it destroyed the SIO chip and shorted out one of the GPU memory drivers and the Audio IC on the 5V rail.

When I plug in power to the laptop and look at the board under my thermal camera, the Audio IC gets extremely hot (~350 F) and I see the 5V coil getting warm (80 F). I still haven't replaced that GPU memory driver that I had previously removed.

The interesting thing is that all of the main power rails are being generated, the CPU VCore is healthy, and GPU memory isn't shorted to ground. My previous post where I mentioned the GPU memory being 9 Ohms was after I applied heat to the board and removed a faulty component. I didn't realize that it took a while for it to return to it's normal resistance. It's Samsung memory so the resistance on it is going to be lower (~20 Ohms). I still get 1.8v on the BIOS chip when power is plugged in and the chip isn't shorted to ground on Pin #8 so we probably have a good PCH (or so it appears).

Wouldn't it be amazing if this was a perfectly healthy board and taking the Audio IC off the board relieves the low resistance on the 5V rail and then replacing the SIO chip fixes the laptop?

Wouldn't hurt to try right?

I'll have an update soon.

[mcplslg123]

Re: ASUS GA401QM Missing 5v

I dont think insering a ram stick with battery connected will damage audio ic/sio as its not related at all. Ram has something to do with memory controller and cpu-nothing else. I think you had a short on 5V rail and these audio etc may got killed.

Anyway, no harm in removing the components. If resistance goes to normal value after removal,worth trying.

[ResoluteHawk]

Re: ASUS GA401QM Missing 5v

So I actually found the cause for this and managed to fix it, but I forgot to update this thread.

The issue where the 5v is a low resistance was actually due to a shorted GPU VRAM driver and one of the Dual N channel MOSFETs associated with it, which gets power from Pin #14 on PU9401. The problem is that if this driver is bad, it will kill either of the Dual N Channel MOSFETs (PQH9402, PQH9404) or both of them. That's why it was killing one of them when power was inserted and thus, I got stumped. Until I realized that the driver was the culprit.

I took off PQH9404 and resistance was back up to 3M Ohms. Great!

Once I took the VRAM driver off the board (PU9401), resistance on the gate of PQH9404 went to OL, which is actually a good thing. After replacing the driver and PQH9404 (again), inserting power now yields a charge light and a good power on, and the gate of PQH9404 and PQH9402 both measure 3M Ohms.

Since there aren't many threads on the ASUS G14 on this forum, I thought that I should update this to let people know that if they have this issue on the GPU VRAM rail, you MUST replace BOTH THE DRIVER AND THE MOSFET.

[Sephir0th]

Re: ASUS GA401QM Missing 5v

And the audio controller has healed by itself?

I suggest to check the GPU in detail, under load with all drivers installed.