iMac's screen won't turn on, external display "works"

[crucius]

Hi everyone!

I've bought a second-hand iMac that was described as having a RAM issue (three beeps). I took the RAM out and put it back on again and the computer boots (I can hear the chime). However, the screen doesn't (black, no light whatsoever).

Since this iMac came without keyboard and mouse, I've used a standard wired keyboard to reset the SMC and PRAM, but that didn't work.

I've connected the iMac via miniDP to my Dell monitor, and I can see the Yosemite background blurred. Thus, I thought: OK, perhaps the iMac is expanding the screen. However, the shortcut to mirror the display (CMD+F1) won't work.

What am I missing?

Edit 1: I've tried to run a Recovery Disk via USB stick, but the screen won't work. If i do this while connected to the Dell monitor, it shows a grey screen, and then a black illuminated screen (but nothing from the main monitor).

The seller assures me that everything was OK with the computer when it started to beep (and I have no reason to believe he is lying)

Edit 2: I've found a wired mouse, and the cursor shows in the external display, but right clicking does nothing.

 

[crucius]

No one has any idea how to solve this?

 

[tyche]

You don't say what year but if it's older and easier to open take a look inside and make sure the cables are properly plugged in.

 

[crucius]

You don't say what year but if it's older and easier to open take a look inside and make sure the cables are properly plugged in.

Hi! Mid 2010. The problem is that I don't have suction cups. And besides, if the problem was the iMac's screen shouldn't I be able to use an external display? The external display only shows Yosemite's blurred background.

 

[crucius]

Ok, I've opened the thing, took the display apart and then re-installed it. Now I can use the iMac normally on the external display, not on the iMac's display.

 

[tyche]

I have a 2010 iMac and back then I added my own SSD. When I put it back together the screen wouldn't come on but I hooked an external monitor up and it worked. So, I opened it back up and found the loose cable and reattached it.

If it's working better, you might need to take a closer look at the cables and make sure they are all properly seated and not damaged.

Other than that, it begins to sound like a more serious issue possibly damaged while being moved.

 

[crucius]

Yeah, I mean i triple checked the connections and they seem fine. However, the LCD cable doesn't look too good, so I'll just buy a new one (28 USD) and see if that solves the problem. If not, I guess it's the display that is dead.

 

[MacVidCards]

There are 2 levels of "dead" display. One is the display not working at all, the other level is just the backlight not coming on. Using a flashlight you can frequently see the desktop is there, just not illuminated.

What you described sounds like it thought that the display was working at first. That the 2nd display was exactly that. At that point it would have been good to do the flashlight test. Using screen sharing would also be a good choice. This could be done using firewire disk mode.

The fact that the 2nd display is now showing up as the first implies that you have further broken the connection and it no longer sees the internal.

A bad backlight is frequently a bad inverter board. These are available from DV Warehouse or Powerbook Medic and places like that. I would guess $30-50.

 

[crucius]

I did try using a flashlight, but there was nothing there (it was one of the first things I did, since it is frequently recommended in this and other forums)

And I don't know if it's relevant, but the internal display doesn't appear in system report.