Asus GL703GM short

[retrorepair2]

I've got the above which had suspected liquid damage (now ultra sonic cleaned) and when RAM is inserted I get the white LED and power button light up and nothing else.

When I remove the RAM I get white light, charging light and it seems to boot by itself, no beeps but keyboard pulses colours and power button is responsive.

The mosfets on the charge line recieve 18v but output 0.835v even though the charge light is on and I've removed a short mosfet (gate was reading 8ohm) below the large inductors under the cpu/gpu.

I've also got what looks like a short on +nvvd but can't find the source.

I've ordered a new mosfet and new ram as I suspect the old RAM was shorted (most caps read 0 ohm) but have the feeling this is a shorted CPU or GPU.

Can anyone confirm if I should see it try to boot if the CPU or GPU is short? I'd like to think it's positive that I'm seeing that?

[retrorepair2]

Re: Asus GL703GM short

Please see attached boardview for areas I've marked up in red, these points are reading 3.7ohm to ground.

Is this normal?

I really wish I had a better resolution image of this, the schematic is great (https://www.badcaps.net/forum/showthread.php?p=1199092) but without this I've no idea where any of the components are.

[retrorepair2]

Re: Asus GL703GM short

So I chanced it and installed some new RAM, it actually booted up! I'm shocked to be honest, but this does give me hope now.

The new mosfet was dispatched today so we will see what happens when that's installed.

I can hear a ticking sound coming from the right hand side around the GPU when it warms up, shortly after this photo it did shut down, I suspect either due to the missing fet or whatever is causing that short. Measuring 2.8ohms in those areas now. It still turns on when power is applied though. I DO think the battery is dead also. Almost everything in this thing was dead, RAM included.

Could I maybe need to replace the power controller IC? I did hear that would need to be replaced if any of these mosfets died, but then the area around it doesn't seem short. I'm pretty much at the limit of what I can think of for now.

[retrorepair2]

Re: Asus GL703GM short

Ok so feeling frustrated, I thought sod it, let's just try installing windows and see what happens. Well, it got almost all the way through then shut off. It did however turn back on and turns on reliably.

That mosfet is obviously still missing, I believe it's related to the video vcc. It should hopefully arrive tomorrow so we will see what happens then.

I dunno, I really don't see how this thing can have 3ohms on the video vcc to gnd and 1ohm on the cpu vcc. It makes no sense to me but then it seems to work pretty well and nothing seems to get overly hot.

[retrorepair2]

Re: Asus GL703GM short

So I found the boardview for GL702 which looks to have a similar looking +NVVDD power generation circuit so I'm going to take a look today and try to narrow my short to a specific rail

[retrorepair2]

Re: Asus GL703GM short

Feeling like I'm shouting into a big hole here but hey, at least I can use this thread to keep track of where I am.

So as far as measurements go, here's what I have on the various power rails that look short to me:

+VCCCORE - 3.3ohm, 0.9v
+NVVDD - 1ohm, 0.8v
+NVVDDS - 2.5ohm
+FBVDDQ - 58ohm, 1.3v
G_PWR_SRC_NVVDDS - 350Kohm and drops to about 50kohm
P_NVVDS_LX2_L_30 - 2.4ohm
P_NVVDS_LX1_L_30 - 2.4ohm
G_PWR_SRC_FBVDDQ - 55ohm

[mon2]

Re: Asus GL703GM short

Low voltage power rails like the CPU and GPU rails will be naturally low resistance to ground, by design. If they are too low, then they are shorted.

When the unit turns off, measure the voltage to ground of each inductor on the board. Checking to see which rail(s) turn off

[retrorepair2]

Re: Asus GL703GM short

Low voltage power rails like the CPU and GPU rails will be naturally low resistance to ground, by design. If they are too low, then they are shorted.

When the unit turns off, measure the voltage to ground of each inductor on the board. Checking to see which rail(s) turn off

Thanks for the reassurance

If you think those readings are ok I'll do as suggested. I understand resistance would be lower but they just seem extremely low. Not that I'm an expert!

I'll check the inductors then. I take it I'm looking for a missing voltage?

Do you think it could be shutting off due to the missing MOSFET in the +NVVDD generation? Maybe it's a bit unstable? I'd hoped the replacement would be here today, so much for 1st class post!

[mon2]

Re: Asus GL703GM short

While I do not have the actual resistance readings of the same devices, they seem to me to be ok.

Be sure that you are not taking resistance checks with power to the logic board. Resistance and diode reading are always with no power to the logic board.

I think it will be good to check for missing power rails when the logic board shuts off.

Then need to check if that local power supply ic is enabled or disabled. A local power rail will shut off if the current draw is higher than expected. This could be from a shorted cap on that rail. With no power, you can check the resistance to ground of that inductor.

Each inductor is linked to a local power rail.

[retrorepair2]

Re: Asus GL703GM short

Great, thanks.

No I know enough to do these measurements without powering the board or battery attached.

I'll see what I find then, though if a power rail disappears, I'll bet it's brief since when it happens, the system powers right back up again. Maybe I'll just attach my probes to the shortest looking power rail then wait to see the voltage disappear if it does.

[mon2]

Re: Asus GL703GM short

it seems to boot by itself,

Often, this is linked to the 2 x DCin mosfets & charger IC operation.

Start with the basics and review each of the DCin mosfets.

What are their markings? Which charger IC is onboard your logic board?

If it is the BQ series (Texas Instruments), then you will have N-channel mosfets and the ACDRV pin of the charger IC should be reviewed.

You may have a leaky mosfet - often the 2nd one in the power path is at fault.

You can check the resistance across the mosfet pins to see if there is a low resistance = defective mosfet.

PS: Need to shovel some wet snow - my favorite pastime. My car is blocked in the driveway. BBL.

[retrorepair2]

Re: Asus GL703GM short

Thanks I'll check that

*edit* Removed that bit, was my bad lol

Also you have snow? It's cold here but thankfully, none of the white stuff

[mon2]

Re: Asus GL703GM short

Yeah - we are somewhat lucky with the snow patterns in our area. Our brother in Toronto got hit with 20-30cm of this heavy stuff. Hope it is the last of the season.

Attached is a view from his front yard (Toronto).

[retrorepair2]

Re: Asus GL703GM short

Ah yeah I'm in North Wales in the UK. We get more than most places but not *usually* this time of year. Always cold here though.

So my thought was since it seems technically safe to run this laptop I'm trying to install windows so it's got an OS at least, but ALWAYS shuts off when it gets to the "getting ready" screen for about 5 mins.

It did occur to me though, I've not got the original charger, I've rigged a generic PSU up to it for testing but guess what? It's only 90w. That's not going to work very well is it?

Also the battery isn't charging, nor the BIOS battery. They could both be dead as most of what came with this machine was, including the RAM (dead shorts all round, crazy).

I get the RGEN 5v on the charging IC (it's a BQ) but can't get to the ACADV to test with my chunky probes. The data signals SDA, SCL and the other one with a test pad (forget the name now) are reading 3.2v and aren't short. The mosfets related to this have 20v on the first one's drain, then .8v on source and gate. None are short or low resistance nor to each other (in the Kohms). One is reading 0ohm vs ground on the drain but according to the schematic it should be. The battery itself is recieving .8v but again, this charger may not be man enough to charge it?

[mon2]

Re: Asus GL703GM short

1) REGN should be ~6 volts. Important.

2) ACDRV should be ~25v to enable the N-channel mosfets. You can measure the same ACDRV voltage at the gate pin #4 of the DCin mosfets.

3) BQ reference designs are always with a ~4k series resistor between the gate pins and the ACDRV pin on the charger IC. You can remove this 4k resistor and check if on the PCB pad if the boosted 25v restores or not.

4) do confirm the ACDET voltage to ground. It is used to enable the ACDRV voltage.

[retrorepair2]

Re: Asus GL703GM short

Great thanks, some stuff to look at then

3) BQ reference designs are always with a ~4k series resistor between the gate pins and the ACDRV pin on the charger IC. You can remove this 4k resistor and check if on the PCB pad if the boosted 25v restores or not.

Trouble is I've no idea where that is, I did try looking for it earlier. If it's gone OC I've no chance.

[mon2]

Re: Asus GL703GM short

Can you share the full markings of your BQ charger IC?

A trick you can use is diode mode. Short the probes and meter will tone beep.

No power to the logic board.

Meter probe on ACDRV pin on charger IC.

Now probe all nearby black body resistors till you hear the beep tone. Part could be on the opposite side of the board. That part is likely to be a 4k ohm resistor.

[retrorepair2]

Re: Asus GL703GM short

I'm an idiot

Of course if ACDRV can be measured at the DCIN mosfet gate then I have one side of it. I'll report my findings in a bit.

The charger IC btw is a bq24780s

[retrorepair2]

Re: Asus GL703GM short

Ok here we go:

ACDRV at the DCIN mosfet gate - 20v
REGN - 6v exactly
ACDRV at the 4k resistor 20v on the mosfet side, 2.7v on the IC side?
ACDET - 2.7v

This is all without battery attached btw

[retrorepair2]

Re: Asus GL703GM short

It's the same with battery attached. Also CMPIN is only reading 0.6v

The mosfets on the top of the board in the path to the battery, one is reading 0.8v on the gate and source, the other 0v on both. Neither are shorted in any way. Confused!