iMac G5 boot to black screen

[Ih8reno]

Hi all


Awhile back I was given an iMac G5 ambient light sensor model. When you press the power button it chimes and seems to read from the hdd. The screen stays black and eventually fans ramp up.

I have tried swapping ram as well as connecting an external monitor (no picture is shown). The iMac for sure was opened up before as around the psu a screw was missing.

The capacitors seem fine as I know this is from when there was an issue with badly made calls.

Anyone have any ideas of what the issue can be?

Any help is always appreciated

 

[DeltaMac]

Do you have a 17-inch, or a 20-inch iMac G5?

There is a row of troubleshooting LEDs near the main fan.
You can power up with the back cover off by pressing the little button close to the main fan.
LED 1 is on whenever power is plugged in.
LED 2 comes on after pressing and releasing the power button.
LED 3 comes on after the logic board activates the video. I suspect that LED 3 never comes on.
Most likely fix is to change the logic board.

There's also an odd possible fix for this, give it a try:
Open the back, remove the optical drive, then try power. If you get video now, you can swap out the optical drive, or just leave it out, if you don't really use the drive.

Be sure to try different memory sticks, not just reseat the existing sticks.

 

[Ih8reno]

Well you are right, led 3 never comes on. I do notice the psu makes a high pitched noise when plugged in as well.

I will see about removing the optical drive.

 

[DeltaMac]

Certainly, a failing power supply could be noisy.
PSU is 15 years old...
It's not impossible that a failing PSU might not provide enough current to activate the video.
It all has to work together.

The swelling capacitor issue was certainly one that affected iMac G5s. I changed a lot of logic boards, back when I worked at an Apple reseller. But, the ALS iMacs were a bit later, and the capacitor issue wasn't as pronounced on those. They weren't directly part of the repair program that we used to repair the original iMac G5s.

Is yours a 17-inch, or 20-inch iMac?

 

[Ih8reno]

Just removed the dvd drive, no dice. I also swapped out the ram with known good sticks. It’s a 20”.

 

[DeltaMac]

I guess you are staring at the logic board, then.
Apple's part number for that was 661-3613 - which can help you search for a replacement MLB.
PSU part number was 661-3625 - if you think that will be a possible fix, too.

 

[Ih8reno]

I’ll have to think about it as I’m not sure it’s worth replacing those parts as it was free. Thank you for your help