iMac G5 black screen

[mitchW]

I received a dead iMac G5 yesterday. It is a 2004 17'' model. When I got it, the unit powered on and chimed, but when the backlight came on it flickered and then the iMac died few moments later.

It had one blown cap on the motherboard which I replaced (1800uF 6.3V Rubycon which I replaced for 2200uF 6.3V Matsushita). I also ran an ESR meter through the other caps, but they all checked fine. Also there were multiple blown caps inside the PSU, which I also replaced (I had all of them available, except for 4400uF 6.3V one, for which I used a 3300uF 6.3V one). The PSU is an "EE" type.

Now the computer boots and runs fine, except for the screen which is black. The backlight is on and can also be adjusted via F14/F15. It has a Tiger installed, I then put it to FW Target disk mode and booted off it, and enabled a Remote Desktop access, so then I was able to test the machine, but the screen is still black.

I have checked all the connections, and the LCD is detected in the System Profiler, but it is still black. Also I reseated the memory modules.

I'll try to hook the iMac to the external display, but currently I don't have the right MiniVGA to VGA adapter.

Any thoughts what else to check?

 

[TheWhiteFalcon]

GPU, try booting it in safe mode. Also check the monitor cables.

 

[mitchW]

I tried booting in safe mode but it is the same. Also zapped the PRAM twice and replaced the PRAM battery. LCD cables look good, and I have reseated the both connectors.

I am afraid that it might really be the GPU, but it has a GeForce FX5200, and I don't remember seeing these fail.

 

[unity]

I would replace all caps. Seems like you know how anyway. Pretty sure this was one of the models affected by the bad cap formula.

 

[uniserver]

yup sounds like the gpu, you could always bake it in the oven, make sure to flood the BGA array with flux, that is K E Y.   people always forget the flux for some reason. 

 

[mitchW]

Update:

Yesterday I got a ALS 17'' G5 iMac from a friend, which has a bad LCD (randomly appearing lines, but desktop could be seen through), but otherwise in working condition. I swapped the panels, and found out that LCD from my iMac is okay, since it works correctly on the ALS. His panel on my G5 shows random lines, but there is no picture seen through, but it works on external display.

So I guess that my motherboard has some issues, I would say that it is probably the LVDS subsystem or maybe the GPU.

Does anyone has the block diagram of the iMac G5 or perhaps schematics?

 

[techknight]

Hm...

Maybe an oven bake?