820-00840 No Boot missing PP5v_S5

[PhilipC]

Board smells of shampoo but cant actually see any corrosion, charger was reading 5v replaced u7000 now reading 20v but 0.03a.
PP5v_s5/4 = 0v
PP3v3_s5 =0v
G3H = 13v

 

[2informaticos]

Any liquid sign around U7800, or CPU?

Check PP3V3_LDO3V and PMIC_SHUTDOWN_L.

 

[PhilipC]

No signs of liquid anywhere near cpu,

PMIC_SHUTDOWN_L = 0v
PP3V3_LDO3V = 0v

 

[2informaticos]

Check around U7800 (7 OF 10), page 60.
As you have two identical boards, compare diode mode readings.

 

[PhilipC]

C738 is measuring low, removed cap and tested same result. Replace U7800?

 

[2informaticos]

I cannot find C738 in schematic...

 

[PhilipC]

sorry C7838

 

[2informaticos]

1V25_VREF is not connected any other place.
So should be bad U7800...

 

[PhilipC]

reaplaced u7800 rails are now up board is using 20v 0.6a then drop to .3a after 10 seconds and stays there
L7210/20 = 0.6v
L7370 = 0.8v
L7410/20/30 = 0v

cpu is getting warm

 

[PhilipC]

ultrasonic and now working.
Thank you for your input

 

[2informaticos]

Graphics voltage (VCCGT) is the last will appear; maybe only under graphics load.
Any way to compare CPU Core voltage (VCCCPU) with a working board?
You don't see liquid signs, but smell of shampoo could mean dead CPU...

 

[PhilipC]

Probably was some stuff under cpu or one of the chips after UC all working

 

[2informaticos]

I suppose corrosion between CPU balls...