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820-3115-B no turn on, low PP3V42_G3H

S

Sr. Robot

Member
Hi, got an 820-3115-B has green light, no turn on. PP3V42_G3H and PP1V8_S0 are low. No signs of water damage. Only fan spin on SMC bypass.

PP3V42_G3H = 3.4v

PP5V_S3 = 5.1v

PP5V_S0 = 5.1v

PP3V3_S5 = 3.3v

PP3V3_SUS = 3.3v

PP3V3_S4 = 3.3v

PP3V3_S3 = 3.3v

PP3V3_S0 = 3.3v

PP1V8_S0: 0.6v

PP1V5_S3 = 1.5v

PP1V5_S0 = 1.5v

PP1V05_SUS = 1.07v

PP1V05_S0 = 1.05v

PPVCORE_S0_CPU = 0v
 
2informaticos

2informaticos

Administrator
Staff member
"PP3V42_G3H = 3.4v"
Low, really???

"PP1V8_S0: 0.6v"
There is the problem.

First compare diode mode reading on L7760 with good board.
If good, post U7760 voltages.
Check R7760/61.
You may need to change the chip...
 
S

Sr. Robot

Member
Diode mode readings on L7760 are good.

R7760/61 Good

Replaced U7760 twice, now:

PP3V3_S4 = 0.6v

PP3V3_S3 = 0v

Replaced Q7800 no change.

P3V3_S4_EN is 0v
 
2informaticos

2informaticos

Administrator
Staff member
Which other voltages did you lose?
Re-check the job you've done.
Be sure didn't generate any short on the board.
 
S

Sr. Robot

Member
With U7760 removed the board quarter fans. Cleaned and replaced U7760 again just in case, these are the voltages:


PP3V42_G3H = 3.4v

PP5V_S3 =0v

PP5V_S0 = 0v

PP3V3_S5 = 3.3v

PP3V3_SUS = 3.3v

PP3V3_S4 = 0.5v

PP3V3_S3 = 0v

PP3V3_S0 = 0v

PP1V8_S0: 0v

PP1V5_S3: 0v

PP1V5_S0: 0v

PP1V05_SUS: 1.05v

PP1V05_S0: 0v


Q7860 looks good, P5V0S0_SS is not present.
 
2informaticos

2informaticos

Administrator
Staff member
You had steady voltages before touching U7760; something happened then.
Check for short on all power rails.
Start with 3V3_S0 and 1V8_S0.

Trigger SMC_ONOFF and check for drop pulse at PM_PWRBTN_L (at same time).
 
S

Sr. Robot

Member
Comparing diode mode with a good board in 0v power rails only PP5V_S3 is low (0.111 vs 0.402 on the good board)

PM_PWRBTN_L is pulsing with SMC_ONOFF trigger
 
2informaticos

2informaticos

Administrator
Staff member
5V_S3 should pulse at same time; check that.
Also compare diode mode readings in opposite direction (black on ground).
 
S

Sr. Robot

Member
Sorry yes,

U2650 pins 1 and 2 are pulsing for about 3v and pin 4 pulses for a few millivolts.

U2660 pins 1 and 4 are pulsing for a few millivolts and pin 2 for around 2v
 
2informaticos

2informaticos

Administrator
Staff member
Check for pulse at voltages from page 22.
Pay atention to series resistors and coils.

Just in case, try known good BIOS.
 
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