2009 iMac 27" A312 power on with chime but no display

[jnicus]

I have a 2009 27" iMac which powers on to a black screen.

Without the graphics card plugged in (no screen attached) iMac does the following:
Powers on
Chimes
Hard drive boot sound
Optical drive noise
Diagnostic led's 1&2 are lit
Fans start spinning

With graphics card plugged in(no screen attached) it does the following:
Powers on
No chime
Hard drive makes a short noise
Optical drive noise
Only diagnostic led 1 is on
Fans start spinning

With graphics card plugged in(screen attached) it does the following:
Powers on
No chime
Hard drive makes a short noise
Optical drive noise
Only diagnostic led 1 is on
Fans start spinning
Black screen
No indication of desktop when I place a flashlight close to the screen
Connected external monitor ..no display

I have tried two graphics cards ATI Radeon HD 4670 and AMD Radeon HD 4850 but no display.
Performed an oven bake on both GPU 's at 200 Celsius for 8 minutes. Tried again with no luck.

Could anyone with further knowledge kindly assist me.
Thank you

 

[theMarble]

...ATI Radeon HD 4670 and AMD Radeon HD 4850

Both of these cards were known for dying. Since the failure points start when the GPU is plugged in, I would go find a different GPU to try. Make sure to either get a pre-flashed card or flash one yourself. You will not see any boot screen or recovery if it is not flashed.

 

[Nguyen Duc Hieu]

I have a 2009 27" iMac which powers on to a black screen.

Without the graphics card plugged in (no screen attached) iMac does the following:
Powers on
Chimes
Hard drive boot sound
Optical drive noise
Diagnostic led's 1&2 are lit
Fans start spinning

With graphics card plugged in(no screen attached) it does the following:
Powers on
No chime
Hard drive makes a short noise
Optical drive noise
Only diagnostic led 1 is on
Fans start spinning

With graphics card plugged in(screen attached) it does the following:
Powers on
No chime
Hard drive makes a short noise
Optical drive noise
Only diagnostic led 1 is on
Fans start spinning
Black screen
No indication of desktop when I place a flashlight close to the screen
Connected external monitor ..no display

I have tried two graphics cards ATI Radeon HD 4670 and AMD Radeon HD 4850 but no display.
Performed an oven bake on both GPU 's at 200 Celsius for 8 minutes. Tried again with no luck.

Could anyone with further knowledge kindly assist me.
Thank you

If you can be sure that the graphic cards are all good, then check the MXM socket.
It may get dirty and need a cleaning.

 

[jnicus]

Both of these cards were known for dying. Since the failure points start when the GPU is plugged in, I would go find a different GPU to try. Make sure to either get a pre-flashed card or flash one yourself. You will not see any boot screen or recovery if it is not flashed.

Good day. Thank you for the reply and information. Could you kindly suggest a replacement pre-flashed GPU model.