Asus N53SV Dead No Power

[grahamw01]

Hi all,

I have an N53SV which is dead. When I plug the adapter in the LED on the adapter goes off. From what I have read this is because the adapter detects a short and cuts off power. I found someone had the exact same issue and they replaced the DC board to make it work again. My concern is that if I unplug the DC board from the motherboard and plug the adapter in, the adapter led stays on, so does this mean the DC board is fine and the motherboard is at fault?

When I got the laptop someone had already looked at it, and I could see a lot of components have been resoldered, and 1 mosfet (CSD17310) had actually been soldered on the wrong way round. I have put it back the right way round and checked all other components, none of them look blown or physically damaged (or the wrong way round..)

Does any one know where I can start looking for problems on the board?

Resistance between + and - power in on mainboard is 14.9kOhm
Resistance on DC board power out (to mainboard, not connected) is 5kOhm
Resistance on DC JACK is 0.5MOhm when not connected to mainboard
Resistance on DC JACK is 14kOhm when connected to mainboard

Thank you for reading and I hope someone can help!

Graham

[khaahk]

Re: Asus N53SV Dead No Power

Measure resistance from the marked point to GND. It should be PWRSRC and have adapter/battery voltage, so it should not show low resistance. If it does then you need a lab PSU to track the short location.

[grahamw01]

Re: Asus N53SV Dead No Power

Measure resistance from the marked point to GND. It should be PWRSRC and have adapter/battery voltage, so it should not show low resistance. If it does then you need a lab PSU to track the short location.

Hi khaahk, thanks for the response, the resistance to ground starts climbing from 9kOhms to about 20kOhms then jumps to 3MOhms and gradually drops to about 0.5MOhms.

This is however with most of the n-channel mosfets (12 of them) on the underside removed. I have removed them because they all show 0 ohms between the source and drain pins, so I have been testing them 1 by 1, I have found 1 with a short between source and drain but still even with this one and all others removed, the tracks are showing 0 ohms, this cant be correct right?

Thanks

[khaahk]

Re: Asus N53SV Dead No Power

If you found drain to source resistance 0 ohm without the mosfet then something else must be in parallel (capacitor maybe) which is shorted, here comes the lab PSU to rescue, search the forum how to use it.

[grahamw01]

Re: Asus N53SV Dead No Power

Do you have a schematic for this board? thanks

[khaahk]

Re: Asus N53SV Dead No Power

none is available

[grahamw01]

Re: Asus N53SV Dead No Power

damn, do you know what other components i could remove to test? I dont know how to use the lab psu.. thanks

[khaahk]

Re: Asus N53SV Dead No Power

Post a picture where do you have the short. I have the mainboard currently at hand.

[grahamw01]

Re: Asus N53SV Dead No Power

please see attached.

They are all measured resistances between drains and gates, it seems where ever there is drain from one to drain from another, the resistance fluctuates repeatedly. It will drop from about 9MOhms to 3MOhms then jump to 0Ohms and rise to about 20kOhms, then repeat.

One picture shows some capacitors that look like they have already been replaced.

I have not yet tested the mosfets that are still visible (near the CPU)

Thanks!

[khaahk]

Re: Asus N53SV Dead No Power

The 6 and 5 ohms resistance is a normal resistance for GPU chip.
Lets assume that bios and EC are fine, then first things that are turned on when adapter voltage is connected are 3.3 and 5V.
Measure resistance from these 3 points to GND and post back results. They should show rather high resistance.

[grahamw01]

Re: Asus N53SV Dead No Power

3: 5.35 kOhm
3AL: 23.8 kOhm
5: 11 kOhm

Thanks!

[khaahk]

Re: Asus N53SV Dead No Power

These seem to be ok. AC adapter is ok? Have you tried another one?
There is a chance that if bios battery has been removed, then the mainboard will boot after power is connected. This means that all voltages will come up at once. Measure all biggest coil resistances relative to gnd. You might find low resistance 4-12 ohms in gpu and cpu coils, all others should be higher (dozens or hundreds of ohms maybe).

[grahamw01]

Re: Asus N53SV Dead No Power

Ac adapter is fine and yes I have tried another one. I have also tried without the bios battery but the adapter just turns off instantly when connected. All CPU/GPU coils are like you said 4-12 ohms, and all others are between 25 ohms and 500 ohms, except closest one to battery connectors shows 10 MOhms but constantly dropping. What about the very low resistances on the mosfets, is this actually okay?

thanks!

[khaahk]

Re: Asus N53SV Dead No Power

Mosfets should not show low resistances, unless there is a leftover charge in gate pin. Or no charge for the P channel mosfet (which you should not have). But you said that removing the mosfets did not change the state of the mainboard, so i am assuming that mosfets are ok. Search online on how to test mosfets with a digital multimeter. You have to charge the gate and then measure wether the mosfet D-S shows low resistance. After discharging the gate, the mosfet should close (resistance in Mohms).
These low resistances on D-S on some of the mosfet pads are ok, they are the lower part of the buck converter and are between load and GND, so they show the same resistance as the coil to GND.

[grahamw01]

Re: Asus N53SV Dead No Power

If all the resistances i have shown are normal then maybe it is just the 1 mosfet I found with a short. This mosfet is on the underside near the cpu, could that cause the adapter to trip?

thanks

[khaahk]

Re: Asus N53SV Dead No Power

Could be.

[grahamw01]

Re: Asus N53SV Dead No Power

silly question then, could it cause damage to plug the adapter in with the mosfets removed? just to see if it will still trip the adapter

[khaahk]

Re: Asus N53SV Dead No Power

If you removed all of the mosfets (high and low side) from one buck circuit, then i think not, but i will not bet my life on it.

[grahamw01]

Re: Asus N53SV Dead No Power

Unbelievable! I plugged it in, it scared the life out of me, I thought there was a spark, but actually 2 LEDs came on! How is it possible the motherboard turned on with no mosfets :O I won't complain, I guess that shorted mosfet is the problem!

[grahamw01]

Re: Asus N53SV Dead No Power

thanks for your help khaahk its really appreciated. I have ordered a new mosfet so I will post results once i've fitted and tried.