iMac G5 Random Shut Down (Tried Everything!)

[coopdog]

I'm working for a small non-profit that builds houses for families well below the poverty line, and we have zero assets.
I'm trying to get an original 20" iMac G5 1.8 GHz running 10.3.5 to work properly again or else it probably goes on ebay "as-is."

Symptoms:
Was working well then would randomly shut down, but was usable.
Now, after trying the following it shuts down after only a few seconds! But occasionally will stay up for a few minutes or more.

What I tried:
Firstly, I ran a hardware diagnostic on Install Disk 3; everything passed. Then I did a clean install and wrote zeros to the HD using the original install disks. Even booted from the CD, it randomly shut down. Obviously a hardware issue.

I then tried the standard PRAM and NVRAM reset, no luck.
Then I took the back off and did the SMU reset and startup from the internal power button and held it until I heard the loud "beep."
I also tried taking out the clock battery for 10 min and the airport extreme card. According to the 4 internal leds, the PMU is fine. I also switched the RAM to another slot.

After multiple random shutdowns during startup from both the CD and HD, I would again do the SMU & PRAM reset. No externals are attached.

Does anyone have any ideas besides replacing the power supply and/or logic board? We really can't afford to go that route...

Thanks so much!

 

[MaxBeagleton]

Memory?

Could be a memory problem. Try popping out all but one. (The one memory module probably has to be in a certain slot.) If it still shuts down, try another module.

 

[CubeHacker]

Open up the back cover, and check the capacitors as instructed here:

http://www.instructables.com/id/Imac-G5-DIY-capacitors-repair/
http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php

The iMac G5's were notorious for having bad caps and can cause the exact problem you described. It actually sounds more like a failing PSU, and the caps can go bad inside that as well.

 

[lostime]

it sounds like a logic board problem. Could be fans not working and its shutting down before it overheats.

 

[coopdog]

Thanks!

Thank you for the great links! I now know what to order. It may only be a $5 fix

Sure enough 3 leaking capacitors, and one bulging. I will be ordering replacements soon and will post the results. I'm glad I didn't drop it off at who would have wantonly replaced the the logic board and PSU.

Are capacitors scored on the top as to leak rather than explode?

Thanks again!

 

[CubeHacker]

I wouldn't worry about them exploding. The vents on the top are specifically created so that if they bulge, the vents open to let the liquid to escape, instead of it exploding.

It looks like the leaking caps are from the PSU in your system. Be careful around there, as there are high voltages inside. Leave the iMac unplugged for several hours before working inside there. Capacitors can store a large charge for a good length of time occasionally.

I would personally replace ALL capacitors on the PSU, but specifically, I would worry about replacing all the ones with the black wrapping - thats the brand that was specifically leaking in my imac. Even if they don't look bad, they may be on the way out sooner or later. Let us know how it goes!