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820-3437 - No display - Fan spinning. Sometimes missing PP5V_S0.

R

ronaldo

Member
Hi everyone.

Dealing with this board that does not display, but fan is spinning, battery is dead. Battery replaced, same issue.
It had battery replaced a few months ago.
It will sometimes not power on and missing PP5V_S0.

99% of the time when it's on and no display, it will have all the voltages present from Power Aliases, but not the LCDBKLT Rail.
Tested on external and a good working screen, no display.
No USB activity.
Please, any idea where I should check next?
Thanks
 
2informaticos

2informaticos

Administrator
Staff member
Do you get VCORE for sure?
What about ALL_SYS_PWRGD in that moment?
Also check U1950 voltage on pins 7 & 3.
 
R

ronaldo

Member
Powering the board without battery PPBUS_G3H goes to 8.59V
With battery fan spinning and PPBUS_G3H goes to 7.89V.

ALL_SYS_PWRGD - 3.32V
VCORE - 1.74V

U1950
Pin 1 - 3.32V
Pin 2 - 3.32V
Pin 3 - 3.42V
Pin 4 - GND
Pin 5 - 3.42V
Pin 6 - 3.42V
Pin 7 -3.42V

All resistors from SPI is ok.
I replaced SPI rom just in case and same scenario. (Original SPI Rom soldered back)
 
R

ronaldo

Member
This skipped from my measurements.
I removed L7630, and it measures very low resistance to ground on PP1V05_S0_REG_R.
--------------------------------------
L7630 removed.
In diode mode
PP1V05_S0_REG_R - 0.017
P1V05S0_LL - 0.177
---------------------------------------
PP1V05_S0_REG_R - 0.13Ω
P1V05S0_LL - 0.177Ω

Do you think that this is beyond repair?
 
2informaticos

2informaticos

Administrator
Staff member
0.017 in diode mode is somewhere between 15-20 ohm.
0.13 ohm is pure short, as 0.177 ohm too; 130 miliohm and 177 miliohm respectively.
Please, read the multimeter correctly; you've probably forgot a "K".

However, PCH coil should give a reading 0.100 aprox (diode mode); 90-120 in ohm scale.
So 0.017 (diode mode) is too low; compare with good board.
 
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