Need help fixing DELL motherboard, (schematic here)

[zaoka]

Dell
N7110


Symptom: dead, no power

On page 36 there is a controller PU12. It provides 3 voltages:

• +5V_ALW_2  This voltage is always ON, its like standby voltage. It works fine.
  
• +3.3V_ALW  Once AC adapter is plugged in, 3.3V works for about 2-3 seconds and goes off.
  
• +5V_ALW  Same as 3.3_ALW, works for about 2-3 seconds.
  

Pin 14 and 27 is used to enable these voltages. If logic level is high voltages should be fine.

The problem is that I have pin 27 high all the time, however, +3.3V_ALW is present for only 2-3 seconds.
I am about to order this IC and replace it.

I just wanted to see if there is anything else that I should check before ordering...


Motherboard schematic: http://goo.gl/sC2NF
PU12 controller datasheet: http://goo.gl/JWGR6

[Niklas]

Do you have an oscilloscope? If so, check if the controller does some switching at all during power up at the midpoints between Q1-Q3 and Q2-Q4. If there is switching activity that end, then it might be some current limiting that kicks in. Check for faulty loads.

[zaoka]

No scope... (sold last month) 

I connected power supply and there is no current overload. Without CPU and memory it has around 200mA on each.
Also I dont see that this IC is using current limiting feature...

[nctnico]

Replace the CMOS battery. If that is dead, many motherboards won't start.

[az113]

Here is a many things in repairing notebooks...
Do you check PL10 and PL11 to the ground for short-cirquit? May be it is a trouble?
Also, double re-check, if the firmware in SPI flash is correct. (if you have an SPI programmer, i recommend you to re-flash a firmware (Backup of existing dump is strongly recommended!!!)