820-3115 fan cycling every 2 second.

Yoel Ren

board came in with symptoms : plug magsafe, fan spin for 1 second, stop. then spin for 2-3s, and loop like that
no corrosion found.
r7402/03 measured good.
when fan is spinning, all_sys_pwrgd and vcore is present.
removing ram will cause vcore to be stable, and fan doesnt cycle at all ( board stay on)
any pointer at this kind of symptoms?