iMac G5 not booting at all

[Ike]

So i was given an iMac G5 iSight 20inch model for free by the stepdad of my girlfriend.

Model was made in 2005, only has the 512mb of logic board ram, no ram was added in the single slot.

He did not know what exactly was wrong with it but he could not get it to start... i did not have time yet to take it apart, although i know how to do that.

i want to share the symptoms that i'm experiencing with you because i have looked everywhere but found no good threads on this subject.

first of all:

i know about the iMac G5's capacitor trouble on the logic boards

i know about the psu failure rate on these machines

So, plugged the power cord in, let it sit for a few minutes before turning it on.

it turned on, did not chime and no video, i can feel the fans spinning, ice cold air comes out.

i can hear something spin up for sure other than the fans. (hdd?)

i can hear one faint 'meep' sound coming from the superdrive... as if it checks for a disk once, then it is silent.

the white power led comes on steady, then fades to about half power and it is not really 100% steady anymore... like it is struggling to find power.

after 30 seconds, the fans come on at full power, while still blowing out a nice good stream of cold air out of the vents.

Then it just sits there... it reacts on holding down the power button... it then shuts off with a light click.

There is no power coming from the usb ports. (the mouse light would not light up)

Already tried to reset the SMU...

also the superdrive will not accept any disks... i can put them in almost all the way and then pushing them in further just makes them come out again by use of some spring in the drive...

Now WHAT could cause this... the psu SEEMS ok right?

i know it's a but stupid to start asking questions before actually opening it and doing some visual inspection...

but i just thought that maybe one of you would have had similar problems once?

Thanks in advance

 

[beachycove]

The isight imac g5s did not typically have capacitor problems.

 

[Macdrone]

I would guess PSU as the isight intel shared the same 115 watt power supply and the one I got smoked and charred to a crisp in the one I found.

 

[krye]

My guess is the power supply too. If the logic was dead, my guess is that you wouldn't see any fan or LED activity.

 

[mcdermd]

I've seen more than a few of these suffer from the same GPU failure that 2006 Core (2) Duo iMacs have with the Radeon GPU separating from the BGA. The design of these machines prohibit "normal" people from dusting them out which eventually chokes it to death. You can check the PSU but my money is on a failed GPU.

 

[Ike]

allright, when i open it up are there the typical g5 leds to look for on the logic board... or is there no such thing on the isight models?

and when the gpu indeed HAS failed, it does not bong because of the 'post check' not being able to see the GPU correctly right?

is there a safe way to 'bake' it back to the board? i know my dad has a temperature controlled Bosch heat gun... that could work right?

if anything else fails i'm just going to sell it for parts with added description of the failure...

 

[krye]

Is this one of those "I'll take it if it works, otherwise it's not worth fixing?"because I see a few logicboards on eBay for under $50 bucks.

 

[mcdermd]

Yeah, there are LEDs on the logic board and yeah, it's probably not posting because it never gets the video signal from the failed GPU.

Some people use the heat gun. The better way is to have someone with an actual reflow station give it a go.

 

[Ike]

Took the guts and completely teared it apart without even breaking the metal tabs on the front bezel.

took out the psu, nothing looked blown or burnt, no burn marks in the case whatsoever.

Took out the logic boards and removed both of the heat sinks. Found two cases of dry cooling paste and found two bulged and vented caps on the logic board!

sound like likely culprits to me

i'll keep you updated.

 

[mcdermd]

Oh, man. Those two on the backside of the bottom heatsink? Those are a b*tch to desolder.

The upside is it will probably work if you do.

 

[Ike]

Spot on sir! Those are the ones.

I'm going to try my best and i'll let you know if it will work again.

 

[mcdermd]

I don't think I've ever gotten those out without drama. If its rough, you may consider clipping the legs of the old ones and soldering the new leads to the stumps.

 

[Ike]

You were JUST ahead of me

i wanted to ask how bad i would get killed here for trying to cut the cap with paper around it to catch up any electrolyte and soldering the new caps to the existing leads...

That seems like an o-k idea?

 

[beachycove]

Try this: http://www.classicmac.net/reference/caps/

Glad you have decided to try to fix it. The iMac G5 gets a bad name because of the first revision's problems, but the late 2005 iSight models were much more solid machines. I bought a refurbished/ upgraded unit after the move to intel was announced. Mine is still in service and has not skipped a beat, running continuously all these years.

 

[Ike]

Thanks for the suggestion! Successfully fixed 3 classic mac boards using that recap method, was not sure if that method was also appropriate for the bigger sized non-smt caps.

When i got the mac i went to pick it up from his home office. I was surprised to see another iSight 20 inch standing there as his daily driver.

Never had enough cash to splash on a 'modern' Macintosh. I have always been a Windows user so it's more or less also a personal goal to get this free mac to run

It's time to get out the pliers and make a mess then

 

[Ike]

Okay... some bad news.

Replaced the both caps with new ones.

reassembled everything... it does the same thing... doesnt boot... everything spins, no video, no bong.

Found the diagnostic leds on the logic board... guess what:

Led 3 - indicating good video communication - comes on for just a tiny tiny tiny moment right after pressing the power button. then stays off.

when the fans start spinning at full power, the red overheating led stays off.

so... i guess the GPU failure was the right cause all along?

 

[techknight]

bake it or heatgun it. Nothin to loose.

 

[Ike]

Exactly. I'm going to try and bake it. Remove all the heatsinks, stickering and ram?