2009 27" iMAC Black Screen

[KALI609]

Hey all,
First post for me. I purchased a used 2009 27" i5 iMac with some vertical stripes on the screen. Removed and baked the GPU. Reconnected everything and got a black screen. Rechecked connections and noticed a loose capacitor and loose transistor near the insertion point of the internal display port. I soldered them back securely but no change. Still a black screen with a start up chime. Back light seems to fire up, keyboard works, all 4 diagnostic LEDs are on, and no image seen on the display despite the back light. Keyboard CAPS LOCK toggle light works and all fans etc come on. I'm wondering if I need to redo the solder on the capacitor and transistor. If I have all 4 lights- the motherboard, video card interface, and LCD connector should all be OK, no? My next step is to de-solder the transistor and see if the symptoms worsen or not. If they remain the same then maybe they need a more secure re-solder. Also, I will replace the vertical sync cable as the copper contacts appear lose. However, the vsync cable should not cause the black screen issue, correct? Any tips people?

P.S. I've reset PRAM, checked all the forms, and the PDF troubleshooting manual floating on the internet - all without any change or more information.

P.S.S. The external display capabilities functions just fine.

 

[Guy Clark]

Try testing the Graphics by disconnecting the Display from the Logic Board and hooking the iMac up to an external display booting using the mini display port on the back of the iMac (mini display port to VGA will be fine) you will need a mini display port to VGA adapter which are very cheap (Don't buy Apple).
If there is nothing on the external display when booting in to macOS then the Graphics are goosed.

 

[KALI609]

Try testing the Graphics by disconnecting the Display from the Logic Board and hooking the iMac up to an external display booting using the mini display port on the back of the iMac (mini display port to VGA will be fine) you will need a mini display port to VGA adapter which are very cheap (Don't buy Apple).
If there is nothing on the external display when booting in to macOS then the Graphics are goosed.

[doublepost=1534727346][/doublepost]Thanks a ton for your reply! So I added a P.S.S. at the end late last night. The external monitor does work, however, I kept the Mac LCD connected. I'll try it out with the LCD disconnected. I'm curious as to why I need to disconnect the original LCD panel though?

Thanks!