Lenovo laptop dead motherboard GS752 NM-C781rev. 1.0 2019-11-25 inscribed at the pcb,

[jamesp]

I have a dead laptop with mainboard model GS452/552/752 nm-c781 rev 1.0, i have initiated troubleshooting with the use of digital multimeter. checked voltage signals up to PM_SLP_S3#, found out that before PM_SLP_S3# signal , a PBTN_OUT#_R signal has 3.2 volt state and after pressing power on, PBTN_OUT#, It drops to logic level zero for around 12 secs and then back again to 3.2v for 6 secs. it will loop like that until you pulled out the adapter power. during loop the PM_SLP_S3 and S4 SIGNAL has no output. (0 volt ) may i ask for help to anyone with this kind of board and same kind of problem. thanks

[Sephir0th]

Bad Power Switch, Corrupt ME, Dead PCH, or something which was missed by measurements/observation.

Is the power switch reacting accordingly after press?

[jamesp]

Bad Power Switch, Corrupt ME, Dead PCH, or something which was missed by measurements/observation.

Is the power switch reacting accordingly after press?

Yes it is, from logic high to logic low then back to high the moment switch was released

[jamesp]

UPDATE : PU500 has the following output
* PL500 has 1.05V
*PL501 ...none
*PL502...none
LDO1 ----NONE ( supposed to be 2.5vDDR Supply )
LDO2...1.8V
pins 1,11,16,29,31 and 36 have a logic high enable signal

my question is...is this a sign of deffective PU500 chip (LV5075BGQV) ?
please advise...thanks in advance !!!

[mcplslg123]

You cant conclude Pu500 as bad yet. first check whether all the Enables are present or not on pin 29/1/11/16/31/36. Then do check all the VIN are present or not. This a multi regulator IC and often it gets partially bad but first the measurements please.

[jamesp]

i already told in post #4, 1,11,16,29,31 and 36 have a logic high enable signal.....of course VIN is present because of PL500 have output, anyway i have checked it and VIN is present

[jamesp]

Update : i already tried several dump bios for this mainboard, but nothing happens. here is my observation...that my SPI ROM chip have no SCLK reading (pin 6) and SDO have nothing as well. i used multimeter and DSO for measurements. please help what am i missing here, why no SCLK and SDO reading? thanks

[mon2]

What is the resistance to ground of the LDO1 rail?

[jamesp]

You mean pin 6 of PU500? well its 150kohm and rising due to capacitor coonected PC520

[mcplslg123]

Since all enables and VIN is present for PU500,logically all LDO rails should be there(as its not shoerted). So worth replacing PU500 before troubleshooting further.

[jamesp]

sorry, it was a mistake. no enable signal for LDO1, that is why there is no voltage output for 2.5v ddr supply. My question is why there is no CLK reading on PIN6 of my SPI ROM chip, i measured it using multimeter and an oscilloscope. no clk input, that is why i cant move on another troubleshooting because reflashing of bios is non sense if my spi rom have no CLK on pin 6.

[mcplslg123]

+3VALW_PCH available? SPI CLK is input to SIO.Try flashing the SIO firmware also. EC_VPP_PWREN also released by SIO to activate LDO1 rail on PU500. So i strongly suggest to flash ec firmware first.