820-3115 green light OK, no boot, no chime

[Cocobill]

Hello!

got this board that worked fine yesterday and now appears dead. I've got green light in the charger, PPBUS_G3H is 12.54V, all main s5 rails are good. I did a visual inspection, no liquid damage but caps C1680, C1681, C1682 and C1683 did not look right, as if the metal part on each side was detaching from the body. I measured all four in beep mode and they are all short circuited!

Should I replace the capacitors and go from there or is the CPU blown and it’s a waste of time?

 

[dukefawks]

Pretty sure there will be nothing wrong with those caps. Why did this board come to you, was this liquid?

 

[Cocobill]

One day was working fine, next day did not boot. No liquid damage visible.

 

[dukefawks]

Check if there is a pulse(s) of power on L7260 when connecting the power.

 

[Cocobill]

I have no oscilloscope, when measuring with FLUKE on voltage mode I get no reaction when connecting the power

 

[dukefawks]

Multimeter may be to slow to catch the pulse so this proves nothing. Check SLP_S4_L for pulse. Did you check all rails for short to GND?

 

[Cocobill]

Went to a friend who has a professional oscilloscope, measured on L7260, no pulse Is the board dead?

 

[dukefawks]

S5_pwrgd present? Voltages on R1800/1/2/3, both sides?

 

[Cocobill]

s5_pwrgd on chip U7941 pin 8 is 3.459V. R1800 pin 1 3.305V pin 2 3.209V, R1801 pin 1 3.305V pin 2 3.030V, R1802 pin 1 3.305V pin2 3.299V

 

[dukefawks]

Resistance to GND on L7260? Missing voltages on R1803? SMC_ADPAPTER_EN present?

 

[Cocobill]

Resistance to GND on L7260 pin1 1.047V, pin2 0.447V, R1803 pin1 3.304V pin 2 3.298, SMC_ADPAPTER_EN on Q7920 pin 2 is 3.439V

 

[Repairable]

Resistance to GND on L7260 pin1 1.047V, pin2 0.447V
typo i gues?
no charger/battery when measuring resistance.

 

[Cocobill]

Measured again although I did not have the board connected to power source. L7260 pin 1 .446 pin 2 .446. I operate with a FLUKE 17B+ and in diode mode there is a small V next to the reading, that's why I wrote 1.047V before, sorry.

 

[Repairable]

no problem just wanted to make sure,

 

[Cocobill]

Resistance to GND on L7260 pin1 .0446, pin2 0.447, R1803 pin1 3.304V pin 2 3.298, SMC_ADPAPTER_EN on Q7920 pin 2 is 3.439V

 

[dukefawks]

Out of ideas on this one, sorry.

 

[Cocobill]

How do we test if it's the SMC chip or not?

 

[dukefawks]

You replace it with another one. Very much doubt it will help unless there was corrosion under it.

 

[Cocobill]

OK thank you Duke