Lenovo Yoga 900-13ISK (NM-A411) - Fan spin, no display

[dfear]

Hi

A customer brought in a "Lenovo Yoga 900-13ISK (NM-A411)" as a dead laptop. I found water damage corrosion on the motherboard, which I cleaned with IPA; and now the laptop powers on.

The current problem is: Fan spin, no display.

I have the schematics for NM-A411 motherboard and have been investigating nets containing EDP_VDD_EN in the name.

The first IC in the relevant nets is PU4. PU4 supplies VIN to PU9. ViN = 8.7V (measured at PU4 pin 20 and PU9 pin 1 & 2).

I think PU9 is faulty. I measured the voltages on all pins of PU9. Results are:

1 = 8.7V
2 = 8.7V
3 = 4.86V
4 = 3.3V
5 = 3.3V
6 = 3.3V
7 = 0V <<-- GND
8 = 0V
9 = 0V
10 = 0V

From my observations, PU9 has the correct inputs, but nothing on the outputs.

Pin configuration for PU9 is:
Pins 1 & 2 are VIN
Pin 3 is VDD
Pins 4 & 5 and DATA & CLK
Pin 6 is VBL_INTERAP
Pins 7 & 11 are GND
Pin 8 is EDP_VDD_EN_R
Pins 10 & 9 are V_BL_LED

Am I right in thinking this IC is faulty??????

Also I can't find the chip anywhere. The IC is marked on the schematic as QZ7250, but on the IC as:

Lenovo
E-001
433

Thanks for any help.

[Techtiger]

Re: Lenovo Yoga 900-13ISK (NM-A411) - Fan spin, no display

trace back EDP_VDD_EN_R voltage on PR80 input side ? U90 pin4 voltage ?

[piernov]

Re: Lenovo Yoga 900-13ISK (NM-A411) - Fan spin, no display

EDP_VDD_EN_R is an input to PU9 (driven by CPU). If the enable signal is not present, PU9 won't produce an output on pins 9/10, that's normal.

Did you confirm the laptop is actually POSTing before troubleshooting LCD circuit?