iMac G5 2.0 20" (ALS), can I fixit?

[didius]

I got an iMac G5 2.0Ghz (ALS) from a friend which doesn't boot.

When I push the power-on button the front light turns on, and the fan starts spinning. I don't hear the happy mac sound though.

After a while the fan starts spinning very hard. All this time the screen doesn't turn on.

I've opened the back and here a look at the interior:

The caps are not bulged and don't appear faulty. When inserting the power cord led 1 turns on, pushing the power button makes led 2 turn on. Led 3 and 4 don't turn on.

What do you think? The person who gave it to me said a computer supplier took a look at it and concluded PSU was broken, but since led 1 turns on I don't think that's the case is it? I know the caps are often faulty on this iMac, but here they appear fine. I know looks can be decieving though. 

 

[TheWhiteFalcon]

Caps in the PSU can be bad.

 

[Macdrone]

And caps on the board can fail regardless of bulging or not.

You cannot use visual inspection on caps.

 

[didius]

Caps in the PSU can be bad.

Wouldn't the iMac refuse to give any signs of life it that were the case? 

Is it possible to check the pinouts of this powersupply before I bust it open? Could someone point me to the correct pinout, I don't know if there is a lot of difference between the models (ALS vs ordinary iMac) in terms of PSU

 

[didius]

And caps on the board can fail regardless of bulging or not.

You cannot use visual inspection on caps.

Okay, I guess I should prepare for a full recap. I see all the caps are Rubycon, aren't these high quality caps? And does this somewhat later version of the iMac G5 still suffered a lot from this bad cap problem?

 

[Sherry Haibara]

It could also be a dead GPU - reflow can help if that's the case. 

 

[matacao]

Extract from iMac service manual:


[SIZE=10pt]• [/SIZE][SIZE=10pt]LED 1 [/SIZE][SIZE=10pt]indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac G5 is connected to a working AC power source. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty. [/SIZE]

[SIZE=10pt]• [/SIZE][SIZE=10pt]LED 2 [/SIZE][SIZE=10pt]indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly. [/SIZE]

[SIZE=10pt]• [/SIZE][SIZE=10pt]LED 3 [/SIZE][SIZE=10pt]indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated. [/SIZE]

[SIZE=10pt]• [/SIZE][SIZE=10pt]LED 4 [/SIZE][SIZE=10pt]lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature. [/SIZE]

 

[didius]

I looked further into the problem.

Using the following pinout I checked the PSU. When trickling the power supply I got all the correct readings. I guess the PSU is fine.

I went to check the motherboard and noticed two things.

1) On the backside one cap connection seems to be bad. I noticed some goo-like material  which could imply bad caps.

2) Strange!

On the motherboard just below the pile of caps there seems to be a missing component. Removed? By whom? Does anyone know what component used to be present here? Is it possible to resolder such a component back in? What do you think?

 

[narwhal2]

I wouldnt trust this, but looking at other imac g5 images, it seems to be one of those ferrite beads wrapped in wire that is missing. (i dont know what those are called though)

 

[techknight]

yea its gone alright. you gotta fix that.