Faulty iMac - Only three LEDs appearing in diagnotics?
Hello iFixit users,
This is an incredible website, and it seems like many users have benefitted from suggestions made by others.
I'm experiencing an issue from an iMac I had willingly bought as a faulty machine. At the time of the machine's sale the seller experienced an intermittent problem with the iMac only sometimes working for days at a time. There would be intervals of time when the iMac would otherwise not boot for a few days.
Removing the iMac's glass screen and front shell, I can see the LED's and cabling clearly.
Only the first three of four LED lights are lit when the machine is powered on. Upon pressing the power button, the hard drive, superdrive and fans will kick into action for 8 seconds, then the machine will turn off and turn on again. This time the machine will simply hang in a constant state leaving the hard drive, superdrive and fans spinning.
I understand that the absence of the fourth LED light leads to indicate that the LCD could be faulty, that the LCD screen cabling may be faulty, or that the logic board itself may be faulty too.
The machine does not chime, neither does the LCD screen come to light or keyboard/mouse seem to be responsive in resetting PRAM or booting with Target Disk Mode or boot-from-CD.
Would anyone suggest I double-check the PSU with a voltimeter, or single out any other components before I resort to the problem being a fault of the logic board?
Is this a good question?