820-00165 pulsing rails

[Aivaras]

Green/orange light
no liquid damage.

It takes 0.02 amps and then jumps to 0.04a. And cycle repeats

ppbus = 8.60v
g3h = 3.445v always stable.
ppvrtc = 3.343v pulses to 3.421v
pp5v_s5 = 5.05v pulse to 3.80v
pp5vs4rs = 0v pulses to 0.038v
pp5_s0 0v pulses to 0.351v
pp3v3_s5 = 3.342v pulses to 0.350v
pp3v3_s4 0v pulses to 0.590v
pp3v3_sus 3.342v pulses 0.064v
pp3v3_s3 = 0v pulses to 0.060v
pp3v3_s0 = 0.010v pulses to 0.130v

 

[JohnB8812]

Does CPU VCore pulse as well?

 

[Aivaras]

cpu vcore always stays 0v

 

[JohnB8812]

Hmm ok inspect very closely for liquid or previous liquid damage near the SMC, U6100, U1950, and U1900. Remove J6100 for sure as well. Also check all rails for shorts might be a short causing the pulsing.

 

[2informaticos]

Check for short on all secondary supplies.
Also check all voltages from pages 57/58.
If nothing found, remove R7551 and report if something change.
See if pins 7 & 3 of U1950 pulses.
Use o-scope if possible; your multimeter is not to good to catch pulses...

 

[Aivaras]

Found shorted cap C7553
Now fan spins but nothing on screen.
no image/backlight
Now itt takes 0.24A.

cpu vcore 1.7V all other rails are present.

tried pram reset nothing.
usb mouse light up

replaced u1900 still the same

 

[2informaticos]

Mouse gets steady light if disconnect/reconnect "on the air"?
Better to test with USB OSX pendrive, with LED Link.

Try new BIOS, with clean ME of course.

 

[Aivaras]

Steady light if disconnect/reconnect.
With new bios still the same.

 

[2informaticos]

USB mouse can trick you.
Test with OSX pendrive.
See if LED Link flashes; that can confirm 100% activity...

 

[Aivaras]

Thanks for help. Was bad u1950.