iMac G4 17" 1.25 GHz Model M9168LLA PowerMac 6,1 introduced in 2003.

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Display not working. Why? What can I do?

Dim gray glow on the 17" screen only. Nothing actually shows up there. However, I have the video output port connected to a VGA monitor (CRT), and this works just fine. I just obtained a cheap used 17" G4 iMac. I would like to combine them to get one good working unit. The original one, with the bad display, has the better processor, hard drive, and RAM, and its case is in much better shape. How would you proceed? What to try first? Switch logic boards? What? How? Thanks for any help.

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Deck the Halls
With tools and Fix Kits

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The bottom of the dome can be removed by first removing the 4 phillips screws on the bottom cover and removing it, then the 4 T10 Torx screws under it. Before fully removing the bottom half, partially open it, and disconnect the IDE cables. Now, swing it down. You can now remove the Monitor, and the Sleep light, and microphone cables. once there are no more cables attached to the logic board, remove the grounding cable from the Dome, and remove the logic board assembly. Then, remove the 6 T10 screws holding the drive cages in place, and remove that (There may be some tape holding it in place that you can remove) now, remove the cage, and swap the logic board and cage assemblies from both computers. If you get no video on the new "FrankenMac" then the logic board may be bad, or have a bad display connector.

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We really need to know the specs on the second G4 to be sure of compatibility. The first one appears to be this:

http://www.lowendmac.com/iMacs/17in-iMac...

It's probably the most unpleasant repairing of any Apple product I have ever seen with the possible exception on the eMacs.

Here's a nice pictorial of the teardown process: http://www.xlr8yourmac.com/systems/iMac_...

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Your right, these can be a pain, i cracked the display on one i had a year or two ago, and the replacement panel assembly was not compatible, so I decided to build it "Headless" I removed the display arm, and panel alltogether, and it outputs video through the Mini-VGA port, and seems to run fine when connected to an external monitor though.

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I would first try to swap the LCD assy before swapping the logic boards since you get video on external monitor from the 1.25Ghz machine so the logic board should be OK. Looks like a LVDS cable problem.

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Good point. Thanks.

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Thank you Chris and Mayer for your help. Mayer, those two links do not seem to work for me. But I did get some info from System Profiler on the two 17" G4 iMacs. The better one (on which the screen is not working) comes up as 1.25GHz G4, 768MB DDR SDRAM, bus speed 167 MHz, with video as GeForce FX5200, AGP, 64MB VRAM, and ROM rev. 2079.

The second iMac (with the working screen) provides less info (it is currently running an older OS, 10.2.8 I think): 1GHz G4, 256MB RAM, bus speed 133 MHz, video identified only as AGP.

Clearly, my preference would be to scavenge whatever parts I can from the slower unit, to get a working video screen on the faster one (which also has the better hard drive and optical drive).

I really appreciate any advice that would help me to identify the specific source of the problem as well as the safest and easiest route to fixing it.

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To help you out, I'll post a partial guide for my iDome, I can't help you with removing the screen (Since mine doesn't have one) but I can show you how to remove the logic board, and drive assemblies. Let me know f you want me to do this.

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(My "iDome" is an iMac G4 17", with the screen assemby removed)

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Thanks again Chris. If there is a reasonable chance that swapping the logic boards would cure the problem, I think that would be a good thing to try first. So, yes, if you can point me in that direction, please post that guide. I am hoping I will be able to work on this tomorrow.

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edwardsneil will be eternally grateful.
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