Hello,

this board NM-B453 came from a previously failed repair attempt with no power, quick inspection shows a dead PQ311 & PQ312, wrong SPI ROM used (GD25LB64 1.8v) and a capacitor installed in PR1007 !!

replaced PQ312 and PQ311 (used AON6414), according to the schematic replaced SPI ROM with W25Q64JV 3.3v and removed the capacitor installed on PR1007, flashed with official BIOS (81BT)..

the board came to life, all powers raised except +VCC_GT @ PL1001 = 0v and no initialization

another quick inspection shows the lack of CPU_DRAMRST# = 0.04v, cutting RC23 raised CPU_DRAMRST# to 1.2v but still no init..

onboard RAM disabled using the straps SO-DIMM Only RC1631 RC1632 (not so sure if correct)

remade to UMA using straps RC1609 to RC1610 & RC1608 to RC1558 and removing PL1401 & PL2401 (also not so sure if correct)

still no CPU_DRAMRST# and no init

made all measurements:

GPU
+3VGS = 3.3v
+1.8VGS = 1.75v
+1.35VGS = 1.33v
+0.95VGS = 0.99v
+VGA_CORE PL2401 = 0.88v
+1.35V_LX PL1401 = 1.33v

CPU
+VCC_GT PL1001 = 0v
+CPU_CORE PL1002 & PL1003 = 0.89v
+VCCSA PL1004 = 0.9v

+2.5V_DDR = 2.47v
+0.6VS = 0.58v
+1.8VALW = 1.76v
+1.0VALW = 0.99v

Signals:
CPU_DRAMRST# = 0.04v
VCCST_PWRGD = 1v
CPU_PROCPWRGD = 1v
SYS_PWROK = 3.3v
PCH_PWROK = 3.3v
EC_RSMRST# = PCH_DPWROK_R = PCH_RSMRST#_R = 3.3v
EC_VCCST_PWRGD = 1v
DGPU_PWROK = VR_VGA_PWRGD = 3.3v
PLT_RST# = 3.3v
SUSACK# = 2.5v
LID_SW# = 3.3v
PM_SLP_S3# = 3.3v
PM_SLP_S4# = 3.3v
SYSON = 3.3v
SUSP# = 3.3v

are these normal ?
VGA_PWROK = 0.24v ?
GPU_RST# = 0v ?
PXS_RST# = 0v ?

+1.05VGS_B_PG = 0v (signal doesn't go anywhere)
+1.0VALW_PG = 0v (signal doesn't go anywhere)
ALW_PWRGD = 0v (signal doesn't go anywhere)
+3V_PWRGD = 0v (signal doesn't go anywhere)

by removing SPI ROM, all CPU phases PL1001 & PL1002 & PL1003 rises to 1.1v something

the wrong capacitor installed in RC1007 made me suspect the phases of the CPU, removed PL1002 & PL1003 and tested from PWM side, 1.1v @ PL1003 but 5.7v @ PL1002

traced it to PWM signals on PU901 (NCP81218M), pin 17 PWM2_2PH = 1.8v while pin 16 PWM1_2PH = 0.24v is that normal or PU901 is dead ??

Update:

1) if only PL1003 is installed (one phase), the voltage became equal on both phases PL1003 & PL1002 so the PWM is working normally and PU901 is alive..

2) cutting PXS_RST#_R signal from the CPU side and pulling up to 3v by installing RC1641 will force the reset and GPU_RST#/VGA_PWROK became 3.3v but still CPU_DRAMRST# = 0.04v

3) there is autostart with the adapter, the board starts when connecting the adapter or LBP (0.500ma consumption) then off after 10 seconds, then start again and keeps on, there is a respond to the button, i can switch on and off..

4) while there is autostart with the adapter, no autostart on the battery when it is connected, if the button is pressed it starts for 10 seconds then off, it will not come on again until the button is pressed..

5) replacing the clocks YC1 & YC2, nothing changed

6) removing onboard RAM completely didn't solve the problem also

7) IO was flashed, still nothing

so, what comes before in the sequence ? resetting RAM or GPU ?

is the processor dead not giving out signals ? the resistances of PXS_RST#_R & CPU_DRAMRST# are all normal

вы написали что не тот биос был, вы уверены что он сейчас хороший потому что было как минимум 2 версии в зависимости от используемого процессора и возможно графики
VGA_PWROK = 0,24 В, это напряжение указывает на проблемы с графикой, я думаю, оно должно быть высоким.