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Old Apr 18, 2013, 06:41 AM   #1
markobb
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Imac 20" early 2009, no picture on LCD

Hello,

i turn on imac, first and second led turns on on logic board, vents went on, but there is no picture on lcd. Ive read that i need to replaced logic board, but i am asking here if there is some DIY stuff to work on, like bad capacitors like on g5 2006 or something like that that i can repair by my selfe or there is no other thing and i need to replace logic board?

Is there any video card issues and so ?
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Old Apr 18, 2013, 06:59 AM   #2
gr8tfly
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If you have an external display, connect it and see if you have video. If none, it could be the logic board.

If it does, then the problem could be the high-voltage supply to the display backlight (it doesn't look like they went LED until the 21.5"). Another way to check is to try shining a flashlight on the display - if the video is working, you should see hints of an image. That indicates a backlight problem too.

I'd have to check on it, but I believe the high-voltage supply (HVPS) probably is on a separate board from the main logic. Check over at iFixIt.com. They have repair guides and also parts.

If not the HVPS, it could be a bad backlight itself. It's possible that might be a separate part in the display. Again, check with IFixit.
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Last edited by gr8tfly; Apr 19, 2013 at 05:28 PM. Reason: typo
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Old Apr 19, 2013, 04:20 AM   #3
markobb
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Quote:
Originally Posted by gr8tfly View Post
If you have an external display, connect it and see if you have video. If none, it could be the logic board.
I wil try this but i need to first buy dvi to vga adaptor

Quote:
If it does, then the problem could be the high-voltage supply to the display backlight (it doesn't look like they went LED until the 21.5"). Another way to check is to try shining a flashlight on the display - if the video is working, you should see hints of an image. That indicates a backlight problem too.
I try this with flash lite but screen is too dark to se anything

Quote:
I'd have to check on it, but I believe the high-voltage supply (HVPS) probably is on a separate board from the main logic. Check over at iFixIt.com. They have repair guides and also parts.
Do you have any link for this repair manuals

Quote:
If not the HVPS, it could be a bad backlight itself. It's possible that might be a separate part in the display. Again, it check with IFixit.
On repair manual says if all 3 leds doesnt blink at start it has to be logical board, mine dont blink, first and second is turned on so power supply and power to logical board is ok , but third led is for video and its not on, and this model has graphical chip integrated on logical board so i dont know if this models have problems with graphical chip and needs to be rebaling or leflowing or it simply dead?
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Old Apr 19, 2013, 06:36 PM   #4
gr8tfly
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If it passes the flashlight test, then it is most likely the inverter. Here's the link to iFixit's repair guide for replacing the inverter board.

Passing the flashlight test: if you have the iMac front panel open [to give access to the internals], you can check the inverter cable and the 4 backlight cables going to the display for a secure connection before replacing the inverter board. My gut feeling is you'll need the inverter, though sometimes reseating cables does work (usually after you already get the replacement part ).

If it fails the flashlight test, you can eliminate the logic board as a culprit by testing for video output with an external display (sounds like you have something to use, but needed the DVI adapter). If there is video to the external display, that leaves either the LVDS cable between the display and logic board, or the display panel itself. Reseating the LVDS also requires opening the iMac.

Unfortunately, I don't have a link to the Apple service manual. Also, I just know troubleshooting steps from experience (except particulars like how many and exactly where the cables are; exact disassembly procedure - those sort of things, as I mostly work with portables). iFixit does a good job in lieu of an Apple service manual. They'll work fine for you.
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Old Apr 22, 2013, 02:10 AM   #5
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Originally Posted by gr8tfly View Post
If it passes the flashlight test, then it is most likely the inverter. Here's the link to iFixit's repair guide for replacing the inverter board.
Its a shame that there is no repair manual for inverter itself

Quote:
Passing the flashlight test: if you have the iMac front panel open [to give access to the internals], you can check the inverter cable and the 4 backlight cables going to the display for a secure connection before replacing the inverter board. My gut feeling is you'll need the inverter, though sometimes reseating cables does work (usually after you already get the replacement part ).
The 4 cables i reconnect but i dont know if in right sequence, although i think ive read that there its no matter in sequence of connecting cables in right socket??

Quote:
If it fails the flashlight test, you can eliminate the logic board as a culprit by testing for video output with an external display (sounds like you have something to use, but needed the DVI adapter). If there is video to the external display, that leaves either the LVDS cable between the display and logic board, or the display panel itself. Reseating the LVDS also requires opening the iMac.
So if there will be picture on external monitor the logic board is ok? Couse in laptops it can be picture on external monitor but graphical chip still needs to be changed or reballing.

Quote:
Unfortunately, I don't have a link to the Apple service manual. Also, I just know troubleshooting steps from experience (except particulars like how many and exactly where the cables are; exact disassembly procedure - those sort of things, as I mostly work with portables). iFixit does a good job in lieu of an Apple service manual. They'll work fine for you.
i Have service manual, where it says for 1st and 2nd leds that its ok power and power supply, but if 3rd led dont blinks(like in my case) it says its logical board

Last edited by markobb; Apr 22, 2013 at 02:21 AM.
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Old Apr 22, 2013, 07:56 AM   #6
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Afraid you're on your own on the inverter board. If you know how they function, you might have a chance, but they shouldn't be very expensive and would be worth while IMO.

The 4 cables' order probably doesn't matter, except for troubleshooting. Tip for next time, though: if a wire isn't very unique, or doesn't have it's own tag, add one of your own. A piece of masking tape folded around the wire and stuck to itself works fairly well (though I would remove them before reassembly so they don't get gooey).

Since it only has the discrete GPU, it handles both internal and external video. Having an image is a good sign the GPU is OK.

I'll have to take a look at the status lights when I'm more awake later on today.

The first step is, if you get a normal startup chime, to do the flashlight test. If that passes, I don't thing the external monitor is necessary (couldn't hurt, if you are setup for it).
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