I recently pulled the same model from a recycle yard, initial symptoms were Powered up and then went into standby (purple light came on). Opened it up and it was going into "voltage protect", little red LED on the bottom left of the power supply board. Found the trouble shooting manual online which listed the voltage specs and from there was pretty easy to find the bad part of the power supply. A few minutes after pulling the board I found the bad diode for the VS supply and replaced it with one that had a slightly higher current rating. Has been working fine for (cross my fingers) two days now. Have you by chance taken the cover off the back to see if this (Voltage protect LED) is occurring also?
Davrand
June 2009