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 Post subject: Disable bad iMac display
PostPosted: Thu Aug 17, 2017 6:49 pm 
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Location: Minnesota, USA
Finally got the cable I needed. Monoprice said they shipped it last week Monday and it arrived yesterday, 8 work days later, or 12 days after I actually placed the order. :|

The good news is I now get a picture on my external Dell monitor, though it took me a while of hard rebooting to get it to show a menu bar on the external monitor (yeah, I tried keyboard shortcuts which didn't work). The not so great news is I have tried several things but I can't get the iMac's [bad] display to shut off. It sits there with a barcode image on the screen. Right now I have DisableMonitor 1.9.2 running. This forces the displays into extended mode but somehow places a restriction on mouse movement so you can't have it accidentally wander into the undesired area. It is supposed to blank the other display but it isn't doing that for me. I looked at various other utilities such as Shades, and ideas such as setting up a black jpg in fullscreen mode on the iMac's display (not sure how I would tell it to show there since I can't actually make out anything on the screen). Shades doesn't work on individual monitors and some of those things aren't really doing what I want which is to shut down the internal screen. I don't think any of these shading things would help since those just set pixels to block light and none of the pixels control is working on that computer. What I really want to do is turn off the backlight. Frankly if it were an easy job I'd just try to see if there was some way I could go in and pull a cable to the backlight.

Does anybody have any other suggestions? I did about30 minutes of web searches. Most of them talk about doing this with laptops which are easy because they have clamshell mode.

Early 2008 iMac


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PostPosted: Thu Aug 17, 2017 6:57 pm 
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Location: NYC
Anything at iFixit?


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PostPosted: Thu Aug 17, 2017 10:09 pm 
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Brightness controls should work to turn off the backlight. If you have access to a laptop it should show you which F# keys are brightness.

I wonder if you opened it up and disconnected the display from the motherboard if it would boot or if it'd blow a POST error.


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PostPosted: Fri Aug 18, 2017 5:10 am 
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Thanks for the suggestion MB. Fortunately this computer came with one of those aluminum white keyboards with FN keys marked for dual use. I had noticed brightness on the keyboard but I had tried it last night with nothing happening so I figured with this particular display issue it wasn't working. It took me a while to figure out how to get the other option of items to work. FN doesn't toggle the mode on and off like caps lock, it modifies it while holding it like a shift key. I decreased brightness somewhat with FN+F1 but as I saw others comment online it doesn't let your drop it very far.

Typical Apple. They allowed later iMacs to go into target display mode so you could use one just as a display but when I read about iMac issues online they mostly relate to display problems and what people need are a target computer mode instead.

I didn't see anything helpful on iFixit, though I guess I could try going halfway through the instructions for replacing the backlight and stop there.


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PostPosted: Fri Aug 18, 2017 5:28 am 
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Limnos wrote:

I didn't see anything helpful on iFixit, though I guess I could try going halfway through the instructions for replacing the backlight and stop there.

Yeah, that's what I had in mind with the suggestion to look at iFixit. Just find the take apart instructions for your model, which should hopefully identify the cable to disconnect for the backlight, and pull that.


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PostPosted: Fri Aug 18, 2017 7:45 am 
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Since you're having trouble getting around, here is a link to "inverter replacement" at iFixit, for the early 2008. Perhaps it will be sufficient just to disconnect the inverter cables, step 10. https://www.ifixit.com/Guide/iMac+Intel ... cement/999

Since there may be high voltage involved, be careful, and I would recommend taping over the open connectors to prevent any arcing.

And here's one for the full backlight replacement. Uses CCFL and may be quite a bit more complicated than just disabling the inverter.

https://www.ifixit.com/Guide/iMac+Intel ... ement/5864


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PostPosted: Tue Aug 29, 2017 8:00 am 
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It isn't a backlight problem, or rather it is. I don't want the backlight. The thing is lit up but unless the computer is is in sleep mode or shut down the display it lit up with bar code pattern on it. It's probably the LCD element or the video card.


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