Black screen but backlight working
I'm having a problem with a 5k iMac 27" (mid-2015). When I turn it on, the backlight comes on, but the screen is completely black and there’s no activity.
An external monitor (plugged in with a Mini Displayport / Thunderbolt to HDMI cable) works, but only after I log in. I can do that by selecting the user and typing in my password blind, although it doesn’t work every time. So I restart it, wait a minute, try to login, wait a minute, then if it doesn’t come on I restart and try again.
When it does work, the computer seems to be working fine. It connects to my wifi (again only after login) and everything is fine, except that the built-in screen is black.
Some background:
A few months ago I opened it up and swapped out the HDD for an SSD (with a kit from OWC). It worked afterward, but some of the backlights stopped working, giving a look like stripes of dimness at the bottom of the screen. I needed to order more adhesive strips before I could open it up and re-seat the ribbon cable, so I left it and never got around to it.
It worked for several months. Then one day the screen went black. I turned it off and back on, and the backlight came up but that was all. I tried resetting the NVRAM, reseating the RAM chips, and then gave up and put it in the garage until I had time.
Yesterday I got it out and plugged it in. To my surprise, the screen came on and it appeared to be working fine! I walked away to grab a keyboard, and when I got back the screen was black again and it hasn’t come on since. I plugged in an external monitor and after a lot of messing around figured out I that I can login blind, and once I do the monitor comes on.
I’m assuming there is a hardware issue, probably connected to something I messed up when I swapped the drive. I’m ready to open it up again but I’m not sure what to look for. What are the likely causes of this issue?
Update: I opened it and checked the backlight and data cable.
The backlight cable slots into its connector very loosely, so it might have shifted when I closed up and that might account for the dimness I noticed. Anyway the backlight is working.
The data cable appears to be connected correctly. I opened its little swing-clamp, slid it out parallel to the board, and everything looks fine. There’s no sign of damage or strain in the cable, its connector, or the receptacle on the board that I can see. I also removed the other end where it connects to the display and checked there with the same result. No visible problem. I reconnected it carefully, closed it up, and turned it on. Same result.
Is this a good question?
4 Comments
I think you should definitely do what you never got around to, and reseat the display ribbon cables and make sure those are all good to go.
by Reed Crosby
@reedcrosby Is that the only thing that could be responsible? I want a good idea what else to check (if anything) before I open it up.
by Robert
@zippity No, it's not the only thing, but I think it's likely.
by Reed Crosby
I have a similar Issue, same symptoms (no image displayed, Backlight working brightens and dims normally) although my external monitor starts to display before login so no login issue. As with original post after logging in if I go to the display settings both onboard display and external display are recognised. For me it started after an automatic update overnight, I was working on it fine one day and put it to sleep the next day I have the above issue. The iMac I have owned from new and has sat on my desk not been knocked / dropped etc, also has never been opened any ideas?
by Dave Rowland