black screen iMac 9,1 but boots in target disk mode

[Sumleilmus]

The display on our iMac 9,1 (vintage 2009) (OS 10.9.5 or so) went black. At boot I hear no chime, but I see a brief 1 cm horizontal illuminated band then just more black screen.

I can boot it into target disk mode. Having done that, I connected it to a MacBook Pro running the same OS
and ran disk repair on it, which said it was successful. Also, I can boot it from the target disk (which is inside the iMac with the black screen).

It will not boot to single user mode (except with a black screen, if at all). It will not boot to the recovery partition (except with a black screen, if at all).

This makes me think the graphics card, the display, or whatever connects the two, or multiple items in that set are toast. I think the graphics card is soldered to the main logic board in this model.

This makes me think I need a very expensive repair or a new machine.

Do you agree? Anything else I should try before reaching for my wallet?

 

[Sumleilmus]

Whew!

I hooked it up to an external display, got it to boot to a gray screen, remoted in with screen sharing, told System Preferences>Displays>arrangement to mirror displays, and now it will boot to the external display.

I still need my wallet, but only for a new display, not for a new computer.

 

[DeltaMac]

Coincidentally, I happen to have your exact iMac9,1 in my home shop, with very much the same problem. I am trying to repair it for a friend.
And, I am struggling to get the video to work.
The screen turns on briefly (less than one second) at boot, then goes black. The backlight is the main problem at the moment, as I can see icons and menus when I shine a bright light into the screen.
Hopefully, it will just be the inverter board, and I have one on order.

Is yours a 20-inch, or a 24-inch? That will make a difference, the 20-inch graphics card is on the logic board. The 24-inch has a replaceable graphics card.

 

[Sumleilmus]

Mine is a 20 inch, and if what you describe is a backlight problem, that's the problem I have. If I shine a bright flashlight at the internal display that appears black, I can see the dock, the menu bar, windows, &c.

What is the inverter board, and is it replaceable on the 20 inch model? If yes to those, where did you order it from?

 

[DeltaMac]

Good, your video is working, but the backlight (which is what gives your screen the variable brightness) has stopped working properly.
Yes, the inverter board is replaceable. It's not too difficult. You can view repair instructions at iFixit.com.
Unfortunately, it did not fix the one I am working on here. I am now waiting for a replacement power supply - also replaceable.
I got my inverter here - http://www.ifixmaccomputers.com/922-8844-inverter-20inch-imac-2009
(make sure that you are OK with the return policy at that site. They are quite restrictive with that - just so you know!)