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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > iMac G5 does not boot

iMac G5 does not boot
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Apr 20, 2012, 05:44 AM
 
I have an old iMac G5, the original model, that is used on occasion. After being turned off for several months, it does not start. The first time I heard the boot sound, but every time after that, I have not even heard that. The light turns on and I can hear the fans and the HDD spin up, but the display does not turn on, and eventually the fans rev to max speed because the OS has not grabbed control of them. I have replaced the PRAM battery. There were no visibly bulging caps on the motherboard. Anything else I should try?
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Apr 20, 2012, 06:21 AM
 
PRAM and SMU resets will sometimes kill this behaviour. Some of these have a reset button on the board.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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Apr 20, 2012, 06:29 AM
 
There is a set of four diagnostic LEDs on the logic board. Take the back off and plug in AC power.
LED 1 lights up when there is power present.
LED 2 should light when you power on the Mac.
LED 3 should come on a little bit after you power on the Mac. This one means the logic board is talking to the display.

Be careful when its plugged into the mains with the back off!
There is a power button on the board on most units in order to turn it on with the back removed. Otherwise you can short the power pins where the main power button is using a screwdriver or metal object to bridge and press them at the same time.

Its worth trying to boot with the optical drive disconnected.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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Apr 20, 2012, 07:07 AM
 
I tried to do both of those things. It never got to the beep, so a PRAM reset was futile, but what I thought would reset the SMU seems be the wrong procedure. I unplugged it, held down the power key and plugged in the power, but it seems that my model should be reset using a button on the motherboard. Will try that next time (I am not at the iMac now, I'm asking for advice so I know what I should bring to try to revive it).

The model is in standard config except for a RAM upgrade to 2 GB. Nothing special plugged in: keyboard, mouse and a Bluetooth adapter, and occasionally a TV receiver.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Apr 22, 2012, 02:16 AM
 
The capacitor problem not only affected the logic boards... it also affected the power supplies. So it's possible that's the issue. (Yes, problem power supplies can still power the system slightly and not have enough power to fully power it.)
     
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Apr 22, 2012, 09:08 AM
 
I know, but the circumstances are that it has been turned off for months and left without power for stretches. The cap problem was boiling over due to heat, and it has certainly not been hot.

Besides, if it is the power supply, I might as well trash it, because I'm not going to buy a replacement for a machine that old in any case
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Apr 22, 2012, 12:02 PM
 
If the above steps don't resurrect it, its either the PSU or the logic board.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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Apr 22, 2012, 06:43 PM
 
Yea... I repaired hundreds of these in the day... had it down to a science.. could do a logic replacement in 11 minutes flat.

Power supply didn't have to be on for long to go... it wasn't uncommon to see iMacs with PSU issues that died after cold boot. Sometimes just from plugging into the wall or the system. Didn't take much on those.

Not to say it can't be anything else... but judging from what I've read... that would be my opinion.
     
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Apr 23, 2012, 03:14 AM
 
I realize that it is quite possibly a hardware error, but it doesn't really matter if it's the PSU or the logic board - I'm not going to replace something like that on a computer that is almost 8 years old. The old iMac is mainly being used as an emergency TV, and I could replace it with a regular TV except for one game: Alpha Centauri, which is not Intel native and never will be. If it really is dead, I'll have to re-buy it for Windows and play it inside a VM when that itch needs scratching.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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Apr 23, 2012, 03:26 AM
 
I'm not trying to convince you to fix it. Just giving you my opinion on what's wrong with it. Personally, unless the fix were under something like $50, I'd junk it too.
     
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Apr 23, 2012, 03:40 AM
 
I eventually go into replacing the caps on those boards. Took a lot longer than 11 minutes then though. I still have a roll of caps around somewhere.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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Apr 24, 2012, 04:33 PM
 
Yes cap replacement on the iMac G5 boards is difficult - too many ground planes taking the heat away from the iron.
You could possibly pick up a used/refurbed PSU.

Failing that, send the PSU to Toasty on badcaps.net - he'll no doubt tear it apart and have it working in no time.
     
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May 1, 2012, 01:43 PM
 
Well, I played with it a bit this weekend, and...it's dead. The third diagnostic light does not come on no matter what I do, which means a motherboard replacement. Ah well - it was almost 8 years old, and it has been running 24/7 for long stretches, even if it has been used sparingly the last two years.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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May 1, 2012, 02:18 PM
 
Do the caps look okay on it? It's possible for caps to fail regardless of whether or not the machine has been on recently.

Also, @waragainstsleep - how the hell did you remove the caps on those boards? We ended up having to put together a really ghetto extra PCB with caps attached to fix my G5 - the caps that were on there were soldered on with lead-free solder, and we couldn't get it to melt at all.
     
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May 1, 2012, 06:29 PM
 
The trick was to apply a force to pull the caps out while you melt the solder. Then use a solder sucker to remoce whatever was left. It was usually quite time consuming.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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May 2, 2012, 01:46 AM
 
All visible caps look good.There is a narrow plastic piece along one side of the board, and pulling that off there is a small circuit board underneath (EDIT: This is the inverter, according to the iFixit guide). That board has some goo on it, but it may just be adhesive, and anyway it's under a semi-transparent brown film, so it's hard to see. There may be bad caps on the opposite side of the board, but it looked tricky to remove.
( Last edited by P; May 2, 2012 at 04:25 AM. )
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
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May 2, 2012, 03:39 AM
 
Its been a while but I think all the caps are on the same side of the board.
I have plenty of more important things to do, if only I could bring myself to do them....
     
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May 2, 2012, 04:24 AM
 
Can't find a good picture of the logic board back, but it seems to sit very close to the backlight, so I doubt that there is space for any big cans on the non-visible side.

Random googling seems to indicate that the issue may be the GPU - the FX 5200 Ultra, which runs infamously hot, and apparently fails eventually.
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
     
   
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