Is it a GPU problem or a Logic Board problem?
iMac mid 2007 20''
Yesterday I pushed the power button of my iMac mid 2007 but the screen remained black.
What I have done trying to solve the problem:
- I turned off the Mac and tried a SMC reset and PRAM reset. The first did nothing, while the second restored the loud boot chime (probably I had turned off the Mac with muted volume).
- I opened the iMac because I wanted to check the diagnostic LEDS. The first 3 LEDS were ON while the 4th LED was OFF. The third LED ON should tell me that the GPU is working fine and the fourth LED OFF should tell me that "the computer and the LCD display panel are NOT communicating".
- To check the GPU (that, according to the third LED, should work) I have connected an external monitor using a mini DVI cable. I couldn't get any signal, telling me that the GPU is having problems.
- To check the Logic Board I booted the iMac Volume on my Macbook in Target Mode. I succeeded to do so. Using Target Mode, I created a small Automator app that plays a song after start up. I shut down the iMac and turned it on again, letting it boot normally. It PLAYED the song, meaning that the iMac is booting fine.
To sum things up:
- The third LED is telling me that the GPU is working. However, I get NO external video signal. This makes me think that it could be a Logic Board problem.
- However the iMac seems to be booting fine! This makes me think that the Logic Board should be OK.
What do you think could be the problem here? Is this a GPU problem or a Logic Board problem? Thanks!
Is this a good question?