820-3115 fan spin a few second, and start again ( looping )

[Yoel Ren]

hi I have a 820-3115 which have fan spin, but it will turn off in a few second, and then start again
ppbus 12.6v
when fan is on, vcore is1.1v then drop to 0.8v
tried replacing r7403/2 ( resistance alr 180 and 150k, should be normal)
tried replacing r7051/2
tried reballing smc
tried replacing isl
still the same..
any idea ?

 

[2informaticos]

Looks like board turns off when boots; at the moment VCORE drops.
Try to start in SMC bypass mode first.
Also try known good working BIOS.

Check for pulse at pin 4 of U2660.

Does the board stays on without RAM?

 

[Yoel Ren]

- I tried looking for how to do smc bypass, but I don't see any answer, is it where you unplug battery, press power, wait 10s, then plug charger, and then plug battery while holding power button ?
if that's what you mean, I have tried it, fan run high, but start looping too
-is bios a component ? can I have the component name because i don''t know the location..
-yeah board stays on without ram
pin 4 of u2660 drop from 3.3v to 0v when the fan stop
r2660 looks a bit off, 0 resistance, so i change it, now it have 9.5k

 

[2informaticos]

"r2660 looks a bit off, 0 resistance, so i change it, now it have 9.5k"
Put back CORRECT 0 ohm resistor!

"is bios a component ? can I have the component name because i don''t know the location"
U6100 is the SPI chip where BIOS is stored.

 

[Yoel Ren]

okay change it back to 0 ohm
already change to at least 3 same board bios, still the same
one thing to note : the green light flicker a bit..

 

[Yoel Ren]

any idea ?

 

[2informaticos]

Put good flux and heat BGA chips.
You can also try replacing SMC.