iMac G5 20" Mid 2005 (I think)

MacGuyFrom1831

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Jan 29, 2019
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Dear respected and honourable members of the forum,

I recently just bought an iMac G5 20”, 1 GB, 250 GB Mid 2005 model (I think) from a flee market. I knew it was defective, but thought that I could fix it or use it as decoration at worst. The iMac has graphical errors at boot up, but the OS system loads fine. Everything in the background works even the DVD (tested with a DVD film). Sound works and it seems just fine, but the screen is all screwed up with checkerboards and graphical errors all over the place. I cannot read what is stated on the screen. All the iMacs were defect, but I choose two that were OK, but the first one was better than the second one and I picked up the wrong one (my fault). But, both had these graphical errors/glitches. I opened the iMac and I was quite nice and clean. I cleaned the whole thing and there was not much dust inside it. There were 9 capacitors that looked bulging. I was thinking about changing these to see if it fixed it. However, I do think that the GPU is at fault. I was able to take a screenshot on the iMac (blind as a bat and I cannot see anything understandable on the iMac screen, so it was a lot of guess work) and transfer it to a USB drive. On the screenshot the screen is all checkered and screwed too.

Is it possible that the problem is only the capacitors? Or is it just the GPU? Ways of fixing the GPU is replacing it, reflowing it or reballing it? I think I will just use this a hobby project of mine. But, what are the chances of me fixing it with the information provided and without having to replace the GPU/Logicboard?

Thank you for your time and thanks for your help
 

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timidpimpin

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Nov 10, 2018
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GPU issue for sure. The capacitor issue will happen eventually regardless. Both the iMac G5 and PowerMac G4 MDD are plagued by this bad lot of capacitors made in the mid 2000s. There are many other non-Apple electronics that used these also.

You could try to re-flow the board, but that is often just a band-aid, and only postpones certain death in most cases.

I would say your most realistic option is use it as a remote system for the rest of it's days so you don't have to deal with the GPU issue. Just face the display toward the wall.
 
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MacGuyFrom1831

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Jan 29, 2019
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GPU issue for sure. The capacitor issue will happen eventually regardless. Both the iMac G5 and PowerMac G4 MDD are plagued by this bad lot of capacitors made in the mid 2000s. There are many other non-Apple electronics that used these also.
Are you sure? And it will not be fixed by changing the capacitators? Can it be due to the capaciators only?
 

timidpimpin

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Yes you can change them, but you need to be a very good solderer. The capacitors will not fix the GPU unless the issue is the GPU isn't getting enough power because of bad capacitors. But if the GPU itself is failing, then capacitor replacement won't help it.
 
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MacGuyFrom1831

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Jan 29, 2019
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Yes you can change them, but you need to be a very good solderer.
I have some professional equiptment and my skills are OK I guess. But, is it a good idea to change these if it is the GPU? Could the issue be just the capaciators only?
 

MacGuyFrom1831

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Original poster
Jan 29, 2019
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Yes you can change them, but you need to be a very good solderer. The capacitors will not fix the GPU unless the issue is the GPU isn't getting enough power because of bad capacitors. But if the GPU itself is failing, then capacitor replacement won't help it.
Exactly! I think I need to do a ASD test on it... But I cannot read anything on the screen.
 

galgot

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May 28, 2015
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Strange, cause as you managed to take a screenshot , i would guess the screenshot itself wouldn't show checkerboards...
I have a Macbook pro with defective GPU, displaying arctefact on screen, but a screenshot show perfect image when opened on another machine.
Note old macs , like the Classic or SE, display checherboards (big.) when they have bad capacitors.

Edit: ok, edited post from @timidpimpin explain it all :)
 
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timidpimpin

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There are USB GPU's out there. You could always buy one from a place that allows returns, and use it to help you use the GUI. It will really help you narrow down the issue. I'm not sure if one will work without drivers though. It would need to for ASD tests.
[doublepost=1548775883][/doublepost]Or... try connecting an external display to the iMac directly.
 

MacGuyFrom1831

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Original poster
Jan 29, 2019
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Strange, cause as you managed to take a screenshot , i would guess the screenshot itself wouldn't show checkerboards...
I have a Macbook pro with defective GPU, displaying arctefact on screen, but a screenshot show perfect image when opened on another machine.
Note old macs , like the Classic or SE, display checherboards (big.) when they have bad capacitors.

Edit: ok, edited post from @timidpimpin explain it all :)
I just tried taking some screenshots with the key combinations and somehow with some luck got it transferred to a USB stick. The screenshot is checkered as well and not only the screen. Does this mean that it is a GPU or capacitor problem?
[doublepost=1548776413][/doublepost]
There are USB GPU's out there. You could always buy one from a place that allows returns, and use it to help you use the GUI. It will really help you narrow down the issue. I'm not sure if one will work without drivers though. It would need to for ASD tests.
[doublepost=1548775883][/doublepost]Or... try connecting an external display to the iMac directly.
I thought about the external screen myself, but I Cannot find a cable that fits the video out? Is it a Mini DVI or a mini VGA?
 

timidpimpin

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It has a "Mini-VGA (Composite and S-video with adapter)" according to Mactracker. For the record... I have never owned or even used an iMac G5. I'm just using general experience and common sense to help you.
 

MacGuyFrom1831

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Jan 29, 2019
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It has a "Mini-VGA (Composite and S-video with adapter)" according to Mactracker. For the record... I have never owned or even used an iMac G5. I'm just using general experience and common sense to help you.
Your help is very valued my friend :) I wish someone could answer the question whether it makes any difference that I took a screenshot with the checkers on?
 

timidpimpin

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Your help is very valued my friend :) I wish someone could answer the question whether it makes any difference that I took a screenshot with the checkers on?
I would say it does make a difference. But what difference that is baffles me. It shouldn't show in a screenshot because it's a hardware issue of some sort, and a screenshot is a software task.
 

MacGuyFrom1831

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Jan 29, 2019
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I would say it does make a difference. But what difference that is baffles me. It shouldn't show in a screenshot because it's a hardware issue of some sort, and a screenshot is a software task.
Exactly! That is the confusing part! But what is the answer to this question?
 

AphoticD

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It is definitely a failing GPU. Permanent artifact like that are typically failure of the video memory. Which is why you see it in the screen shots. The video framebuffer itself is corrupted.

Just a thought, but can you get a clear image at a lower display resolution?

The only solution would be to replace the logic board. Somebody here with more iMac experience (than me) could confirm if the logic board from a 17” 2004 model can be installed in the 20” base.

If so, this could present a more economic solution than trying to source the (more rare) 20” parts.
 

MacGuyFrom1831

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Original poster
Jan 29, 2019
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It is definitely a failing GPU. Permanent artifact like that are typically failure of the video memory. Which is why you see it in the screen shots. The video framebuffer itself is corrupted.

Just a thought, but can you get a clear image at a lower display resolution?

The only solution would be to replace the logic board. Somebody here with more iMac experience (than me) could confirm if the logic board from a 17” 2004 model can be installed in the 20” base.

If so, this could present a more economic solution than trying to source the (more rare) 20” parts.
I just read about it and it seems that it could be faulty video memory modules or due to faulty power (capacitors). I noticed that all the artifacts disappeared when there was a total blue background (mouse pointer was still corrupted).
 

tigerintank

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Jun 16, 2013
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You might consider that the psu could be problematic too.

On mine the logic board caps have never bulged but the psu ones did. I replaced those with one of the kits on the web. Psu lasted a short while before giving up the ghost completely - not sure if poor soldering or what.

In any case I decided to go the external atx psu route and bought a cheap 400w one. That lasted a good number of months before failing - got a warranty replacement and went for a better specd one. The replacement has lasted a few years now and still no bulging caps on the logic board...

So my guess is that the logic board is maybe out of spec due to the caps, even though not bulging, and so the demand on the psu is higher than expected. By going to a higher spec psu I'm able to get away with it.
 
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galgot

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May 28, 2015
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Stupid question maybe... have you tried resetting the SMU (like PMU on G5s) , there is a button to press on the logic board.
Still, don't understand why the screenshot itself is checkered ... You can also try to access it via VNC, see if it's checkered too .
 

MacGuyFrom1831

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Original poster
Jan 29, 2019
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I somehow managed to install my WIFI on the mac. Is there a way to install some VNC software on the computer? I'm trying but I cannot see what I cam doing?
 

MacGuyFrom1831

macrumors member
Original poster
Jan 29, 2019
43
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Stupid question maybe... have you tried resetting the SMU (like PMU on G5s) , there is a button to press on the logic board.
Still, don't understand why the screenshot itself is checkered ... You can also try to access it via VNC, see if it's checkered too .
I somehow managed to install my WIFI on the mac. Is there a way to install some VNC software on the computer? I'm trying but I cannot see what I cam doing?
 

Amethyst1

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Oct 28, 2015
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I somehow managed to install my WIFI on the mac. Is there a way to install some VNC software on the computer? I'm trying but I cannot see what I cam doing?
Leopard has Screen Sharing built in which makes the iMac act as a VNC server you can connect to from other machines. You'd have to make your way to System Preferences -> Sharing and turn it on.

Do you also get corruption when you do a "Safe Boot" by pressing and holding the Shift key directly after powering on the machine? The GPU driver isn't loaded in this case, which might also explain why you managed to get through Leopard's installer without problems. If the screen is fine without the GPU driver, you can delete its kexts to prevent it from loading when you boot normally. This means you'll not have any graphics acceleration though and is, at best, a sub-optimal workaround.
 
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galgot

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May 28, 2015
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I somehow managed to install my WIFI on the mac. Is there a way to install some VNC software on the computer? I'm trying but I cannot see what I cam doing?
In System Preferences -> sharing -> Screen Sharing. when activated, should be visible on another mac on the same network , screensharing.
 

MacGuyFrom1831

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Original poster
Jan 29, 2019
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Leopard has Screen Sharing built in which makes the iMac act as a VNC server you can connect to from other machines. You'd have to make your way to System Preferences -> Sharing and turn it on.

Do you also get corruption when you do a "Safe Boot" by pressing and holding the Shift key directly after powering on the machine? The GPU driver isn't loaded in this case, which might also explain why you managed to get through Leopard's installer without problems. If the screen is fine without the GPU driver, you can delete its kexts to prevent it from loading when you boot normally. This means you'll not have any graphics acceleration though and is, at best, a sub-optimal workaround.
I tried what you said and the result is the same. However I am able to read things a little better and now able to start the built in VNC I think. Maybe it is a capacitor after all?
[doublepost=1548784081][/doublepost]Now I've somehow logged into the computer and took a screenshot for you guys. And surprise surprise! The VNC screen is checkered as well as the original one!
iMac G5 VNC.JPG