Hello there, I've found this fault listed for the model, though it's a bit lacking in detail: it simply says: Erratic readings at U507. Replace mainboard.
I found some forum entries reporting U507 s/c and others saying it's giving odd readings, but seems whoever made the posts was unable to find out what the part is as no circuit available, so replaced mainboard with 2nd hand one to fix set. Also says U507 has 1084 printed on it, so perhaps it's an LT1084 which makes it a 5V adjustable LDO regulator...
