Dell N7110 FETs are getting hot

[hazardus]

Hi guys,

I've this N7110. It doesn't turn on because there is a short somewhere.

So 2 mosfets are getting really hot.
PQ11 and PQ12. I changed PQ13,PQ12,PQ11 but still PQ11 and PQ12 hot.
There is a short somewhere but I can't find it.

Any advice and suggestions will be greatly appreciated!

[dj_ricoh]

Re: Dell N7110 FETs are getting hot

take them bot down and see what pads are shorted!

after you you will find what line its shorted

[khaahk]

Re: Dell N7110 FETs are getting hot

If you got PWR_SRC shorted then it could be anywhere all over the board. Use lab power supply to find the short.

[hazardus]

Re: Dell N7110 FETs are getting hot

take them bot down and see what pads are shorted!

after you you will find what line its shorted

Here is the problem. I removed them from the board and I don't know how to find the shorted pads.

PQ11
1-3 pins - 263K
4 pin - 46K
5-8 pins - 94K

PQ12
1-3 pins - 1 Ohm
4 pin - 98.3K
5-8 pins - 94K

These measurements are to the ground.

If you got PWR_SRC shorted then it could be anywhere all over the board. Use lab power supply to find the short.

Can you explain me how to find the short with lab PSU?

Thank you.

[hazardus]

Re: Dell N7110 FETs are getting hot

More measurements:

PL1 19 Ohm
PL5 1.1 Ohm
PL6 1.1 Ohm
PL7 33 Ohm
PL9 10 Ohm

[khaahk]

Re: Dell N7110 FETs are getting hot

Remove CPU from and remeasure PL5, PL6. Search the forum for lab psu method.

[hazardus]

Re: Dell N7110 FETs are getting hot

khaahk thank you.

[hazardus]

Re: Dell N7110 FETs are getting hot

I managed to find a shorted cap under the cpu socket C126 was sorted.
I put back everything and there is still short somewhere but no short anymore on PQ12 1-3 pins.
PL5, PL6 shows normal resistance now.
PQ11 gets really hot quickly.

[hazardus]

Re: Dell N7110 FETs are getting hot

There was a short on PQ12 1-3 pins again. I found another bad cap it was PC37.
I checked the diagram and that cap is only 2V cap.
PQ12 1-3pins has 5V? I changed that cap twice but it's still getting hot. I believe that 5V is killing it.
When that cap was shorted I set the PSU 1V 1A PSU showed 1A when I turned it on. I replaced the cap now it's shows only 0.1A so there is no more short on that line.
I'll remeasure PL5 and PL6 tomorrow.

[khaahk]

Re: Dell N7110 FETs are getting hot

Did you install PC37 with right polarity, for VCC_CORE the 2V cap is ok. Or it gets too much voltage, then you should check PQ1 or PU1...

[dj_ricoh]

Re: Dell N7110 FETs are getting hot

Polarity no .
Wrong value of the cap maybe.

[hazardus]

Re: Dell N7110 FETs are getting hot

Did you install PC37 with right polarity, for VCC_CORE the 2V cap is ok. Or it gets too much voltage, then you should check PQ1 or PU1...

Yes, I did. Now I checked everything without CPU. PL5 and PL6 11.3 Ohm.
Isn't that too low?
PL1 18.3 Ohm.
I double checked everything. There was no short on that rail so I put back the FEts. Guess what? Short somewhere again.
I took down those FETs again. Now another cap shorted. C127 at this time.

Polarity no .
Wrong value of the cap maybe.

Everything looks fine there now. There is another cap now which is shorted after I put back the FETs.
I don't really understand what's going on there.

[hazardus]

Re: Dell N7110 FETs are getting hot

Alright. I replaced that cap. PC37 gets hot really quickly. I set my PSU 5V 0.2A.
It shows short somewhere but this time I don't know where. I checked that cap and on the negative side I measured 5V. I have no idea why. There shouldn't be 5V right?

The other thing is I replaced that "special" cap with the same capacitor just no GND under the capacitor.
I don't know what kind of capacitor that anyway.

[hazardus]

Re: Dell N7110 FETs are getting hot

I found a good capacitor and replaced the PC37 so there is the right capacitor now.
Still short somewhere. There is a big voltage drop on PQ13 pin 5-8. Tomorrow I'll remove PQ13 and check those pins to ground.

[hazardus]

Re: Dell N7110 FETs are getting hot

There is a short as soon as I connect the charger to the board.
I'll change RT8206(PU12) but first I'll remove PU1.
PU12 and PU9 warm PC36 really hot. I've changed PU9 but that didn't change anything.
PQ13,PQ12,PQ11 doesn't get hot at least.

[hazardus]

Re: Dell N7110 FETs are getting hot

I figured out the short problem. PQ1 was the problem.
Now the motherboard turns on but CPU doesn't. I hear some click noise around the CPU but I can not figure out what it is. Could it be a bad CPU?

[khaahk]

Re: Dell N7110 FETs are getting hot

If PQ1 was shorted then cpu is probably dead.

[hazardus]

Re: Dell N7110 FETs are getting hot

When I turn it on I can hear a click noise but I'm not really sure where it's coming from.
Do you think that CPU is dead and that's why there is no voltage at CPU? If cpu can be shorted then that's why I can hear that click noise. Probably cpu vcore cuts off. I can see on my scope it's trying to start but then it cuts off. Anyway I can't turn it off with the power button just if I disconnect it from the PSU or turn the PSU down.

Without CPU I can turn it on and off.

[goontron]

Re: Dell N7110 FETs are getting hot

shorted CPU.

[hazardus]

Re: Dell N7110 FETs are getting hot

It's not the CPU. I got a replacement and it's doing the same thing. A click sound and I can't turn it off.