Another iMac G5 with a black screen.

I have an iMac G5 17" isight that doesn't display video. The screen has a dim glow and responds to dimming, so I believe the backlight is functioning. An external monitor does work but the built-in screen remains black. Reset PRAM and SMU with no effect. First three diagnostic led's come on. Opened it up and the capacitors appear fine to me. Any ideas what the problem is?

Update

I have a TMDS cable on order as I suspect that may be the problem with mine. I'll update to let you know how that goes.

Update

I tried the new TMDS cable and the problem persists. I suppose my next step will be to try a new inverter unless anyone has a different suggestion.

To help narrow things, can I assume the GPU is good since the VGA port is working?

Answered! View the answer I have this problem too

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If your external monitor is working the GPU is fine. I have no idea why you replaced the cable, it was never mentioned.

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Thanks for all the help. In my research elsewhere, there were cases with the same symptoms as me and the cable was at fault so I tried that first because it was cheaper and easier.

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It sounds to me like your inverter may have failed. I would replace it. The correct Apple part number is 661-3841. iFixit has a part however the number is incorrect. A simple web search will uncover that prices on this board run from $23.99 to $100. The repair guides on this machine do not cover the inverter. I will see if I can find a guide that will work for you.

UPDATE

This guide should work: iMac G5 17" Model A1058 Inverter Replacement

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Thanks for the info. Just to clarify things for me, would the backlight work if the inverter was bad? I turned it on while I had it open and can confirm the backlight is indeed working. I had the impression the backlight wouldn't work if the inverter was bad.

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Defective CCFL backlight may have the following symptoms: Screen flashes on red/pink and goes off. Picture stays on in red and slowly be come normal. Picture flickering with dim display. Picture flickering on and off. All these symptoms indicate that the LCD backlight lamp (CCFL Lamp) has reached the end of its life.

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Sorry to keep dragging this out. I feel like I'm not making myself clear. I'm trying to determine if it is in fact a bad inverter. I am sure that the backlight is working fine. What I would like to know is is it possible for the backlight to remain on in spite of having a bad inverter? Thanks.

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If I had the machine in front of me I might be able to tell you more, but I don't.

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Patrick will be eternally grateful.
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