Asus G75VW laptop motherboard failure

[DivineChaos]

Hey guys!

About four years ago I had my gaming laptop at the time have a fan that went out on it. It started making a lot of noise and was unbearable, so I decided to take it apart and "lube" it. I had previously done this on a desktop GPU that had a noisy fan. (I drilled a small hole into the middle of the fan and dropped a bit of oil inside it, and it worked).

Well, for the laptop fan, things didn't go so well, and the drill tip went to far and busted the windings of the motor. At that time I did not have the skills to rewind the motor, so I had decided to look online to find a replacement. I could not find a replacement anywhere at the time so I decided to buy a generic fan to put in there.

I found one to put in there that fit suprisingly well, but the power connector was (probably obviously) not correct. So, (foolishly) I decided to use my, at the time, very crummy soldering iron and my crummy soldering skills, to wire an external switch to power the fan from the main battery pack input from a (if I can remember correctly) a 5v or 12v pin(if needed, I can attempt to re-measure where I soldered from, but I think that's moot). It worked, but I had to adjust the location of the
switch a few times and during the adjustment, the wrong end of the wire came loose and sparked across a few unknown spots on the motherboard.   

Now, several failed attempts later and after having had sent it to a local computer repair shop (for them to hopefully rule out a failed CPU RAM and GPU) and having them tell me "its the motherboard man" (duh), (and having them steal my power brick and replace it with a broken one that I just now discovered years later  ), I am here to give it an actual thought-out attempt with new skills, new tools and new brains to find out whats wrong.

So guys.. Where to start?

What it does:

Power button pressed > Green power light.

nothing else. No fan, no screen flicker, no hard drive ticks, no beeps. Absolutely nothing but the power light being on.

Pressing and holding the power button after pressing once > nothing.

The only way to "turn it off" at that point is to remove the battery pack.

What I have done to "resolve" the problem:

Removed the GPU and pressed the power button > same behavior as above

Removed the RAM > same behavior

Removed the CPU > same behavior

Tried several combinations of CPU GPU and RAM, including none of them> Same behavior

Tried different RAM > same

Scanned every inch of the motherboard with bright light and a magnifying glass for literally HOURS > Found discolored solder points on a ground pad with several "balls" on it. There are several others on the board and they are all pristine except the one. It really looks insignificant, but if I shorted a specific power rail to ground, perhaps I blew that circuits ability to provide that power.  we'll see.

Probed several "fuse looking objects" on the motherboard for continuity > did not find any "opens". (they are small SMD devices that look like resistors but with a single "0" right in the middle of them) Perhaps there are other "fuses", but I am no expert here.

Sent to computer repair shop > they told me motherboard and stole my power brick.  (yes it definitely worked before I sent it to the "experts")


SO as it stands, I have a "bad motherboard" with a "bad power brick". I have an alternate brick for my new laptop, but I am afraid to stick it into this motherboard for fear that it may break my only brick left. (I have determined shorted FET's in the old brick, which I may go about fixing, but MEH... The brick is really bullshit designed with white silicone shit all over the solder pads and its VERY difficult to remove anything at all. (pics on request))

There are TONS of "test points" on the motherboard, but hell, without a schematic, what good are those huh? It's obvious when you look at them that they are points at which a "bed of nails" had pressed against the board for testing. Its like there is a leftover "residue" around the points where you can see that "something" pressed against them. Plus they are labeled for example PJP8700 or PJ8100. Those "ground pads" are also labeled like this: H6507 H6527 etc..  H6534 is the one in question

As a learning experience, I am definitely open to the challenge of fixing this thing within a relative amount of $$. I'm not as broke as I was before and knowing that I may have to spend around $300 to repair this board (for a complete replacement, or replacement of several or a few components), I am no longer intimidated.

Where should I start?

What am I looking for really? There's no "magic smoke" components anywhere on the board at all.

High res, up close pics are available upon request.

[poot36]

On most laptop motherboards the surface mount fuses are labelled FXXX (where the X is a number and there may be 1 2 or 3 numbers).  The fact it turns on is somewhat good.  Most power bricks will shut off if what is connected to them tries to draw more current then they can provide.  I would start by fixing the charger and verifying its output with a meter before plugging it into the laptop.  I want to see if the battery charging circuit is working or not.  You clearly have voltage going to the power switch and power led so that is good.  I would check the voltages on all inductors (labelled LXXX) as these are the outputs for the switching converters in the laptop.  You should see the 19V for the power brick, sometimes 12V for the LCD, 5V for logic, 3.3V for logic, 1.8V to 1.5V V for RAM, and around 1V for the CPU and GPU.  You may find other voltages as well depending on the various chips in the laptop.

[DivineChaos]

I will have results for you in a few hours time. I found another brick that I can use. Thank you for the quick response.

[poot36]

If you look at the motherboard there should be a sticker or silkscreen of the motherboard manufacturer and model number.  Try looking those up for a schematic.  By the way if the laptop CPU does not support integrated graphics when you take out the GPU card the laptop will power on but will not beep or do anything else.  But you should still be able to hold the power button for 4 sec or so to shut it off.  If you do find the schematic I would start by testing the safety shutdown pins on the keyboard controller chip.  If they are telling the chip to disable the voltage regulators then you may have found the problem.  The keyboard controller chip in most modern systems handles battery charging, charging led, power switch, power led, some voltage regulators (usually 5V, and 3.3V, and 5V or 3.3V standby), various wake system from sleep or power off modes (WOL etc), BIOS chip interfacing, and a few other functions depending on the laptop design.  It has a micro in it that is always running watching for you to tell it to try and turn on the rest of the system.  If it is bad then you will have to find a replacement and reprogram it through the keyboard connector.  It is usually 100+ pins so not a job for a beginner.  Good luck repairing the laptop.

[DivineChaos]

So far, there are no components on the board that start with F or L. The inductors are obvious though.

A thorough search for a schematic reveals no result.

PN: 60-N2VMB1600-C03(C03) G75VW

G75VW MAIN BOARD
Rev.  2.4

So the other brick was bad too, but the battery has power still. Fully charged at 15v.

I have probed around the board for some things to start with and I see some of the PJPXXXX points have 15v some have 5.1v some have 3.3v some have 1.5v and several have 0v.

I'm going to take some pictures near the ones that have 0v

Pressing the power button and holding will not power it off.

[poot36]

Some of the points may be ground.  You can check this by setting your meter to ohms mode and connecting one probe to the point and the other to a known ground (eg power jack cover, usb shield, some screws for the cpu heatsink).  If it reads less then 1 ohm it most likely is ground.  The smd components that have the 0 printed on them are just a 0 ohm resistor to get that trace over another trace.  Most smd fuses are white or green colored and have a amperage rating printed on them.  You should also find some current shunts that have 2 thick traces going to them and 2 skinny traces going to them for sensing the voltage difference between the two thicker traces by the way of a very low ohm (0.1 ohm or less) resistor.