I have recently acquired a dead Powermac G5. The previous owner said that he brought it to the service center and its going to cost ~$600 to get it a new power supply, and that was all that it needed to be able to run again.
Well after getting the unit home. The first thing to do is test it without doing anything. Who knows, it might actually NOT be broken. In goes the plug... Pressing the power button results in... nothing.
So next step would be disassemble the unit. This is the intake fan:
Because I did not have the correct service manual for this unit, I took the logic board out before taking out the power supply. I realized later that I only needed to take out the lower CPU to accomplish this (and yes I did take it out again ... but more on this later). I also read somewhere that there is supposed to be a cover on top of this power supply that is now missing, the service center must have forgotten to put it back. Some of the cables were also disconnected, again, my guess is that the service center did not bother to plug it back in as it is broken anyway.
This is the power supply. It is the biggest computer power supply I have ever seen. The middle connector is as big as a standard 24 pin ATX connector.
This is what's "under the hood" of the power supply.
This is the label stating how much Amps is needed by each line. A standard 600W ATX supply should satisfy these values. The only thing missing is the 25Vsb line. From what I have gathered, only the ADC out (for special apple displays) would use this. At this point I was not too concerned about the 25Vsb line.
This is the whole power supply's internals:
After the past experience with blown capacitors, I was hoping this is another case... No such luck. Poking around with my voltmeter revealed that the fuse was blown. I have a spare 250V 10A fuse that i quickly put in. Who knows, it may just be the fuse. I replace the fuse and then plug it in... poof: smoke comes out and the fuse is blown again.
A Careful inspection of the power supply board reveals that there are switching transistors whose legs are melted, there is also a crack on the board, and that there are more surface mount IC's at the bottom side of the board:
Some of the IC's are burnt too much to be able to read the writing on them. Ok... I was going to try to "component-level" repair this one, but at this point, it looks like it would be more feasible for me to substitute an ATX power supply.
After getting a 550W power supply from a nearby computer store and testing this with a spare PC motherboard and verified everything working, I cut all the wires coming from it, and desoldered the cables from the original G5 power supply board. I connected everything to the corresponding voltage but left out the 25Vsb.
This is how it looked after the operation:
I used shrink tube to insulate the individual wires to keep it clean (electrical tape would leave a sticky residue). After double and triple checking my connections with the voltmeter, I am ready to plug it in. Before I put all the screws back I should test it and see if it actually would work:
So, it's the moment of truth. Plug it in and press power button... Power supply fan runs... red LED lights up on motherboard... but no startup chime. Repeat... same...
Of course (duh). There is no RAM. (double duh). After installing a pair of 1Gb sticks of PC3200 DDR memory (from my iMac G5):
Pressing the power button now gives the easily recognizable apple startup chime, or as a good friend calls it, the "jeng" sound. That's all I needed to hear, out comes all the cables, out comes the 2nd CPU... put the power supply and everything else back on...
And it all works. Both CPU's detected, About this mac says it's a "Dual 2 GHz PowerPC G5". I did notice it was a bit noisy. My wife described it to a coworker as "it's as if there is an airplane about to take off". After doing some more reading, I think I may have put the processors back the wrong way (swapped the 2). The logic board seems to "remember" the CPU ID of what was there before, and keeps a thermal profile stored in non volatile memory. This thermal profile would be specific to that particular CPU. If you were to replace any of the CPU's (or like what I did, swapped the 2) the logic board was programmed to "play it safe" and spin the fans (all of them) at full speed. I have 2 options, take the CPUs off and swap them back (no way). Or run what is known as "thermal calibration". Running thermal calibration took about 30 mins (about 15 mins for each processor), after which the fans are running at their normal speed now.
After all that I used the computer for a few days, and noticed that the power LED was not lighting up. It wasn't lighting up either during sleep (it's supposed to look like it's "breathing"). After taking out the front panel connectors and power switch, testing the LED reveals that there is nothing wrong with it, nor with the cables connecting it to the logic board. The only thing that could be wrong would be, apple must have used the 25Vsb line for the LED. I found a 24V switchmode power supply at a local electronics store, and after taking out the power supply again, I was able to put it inside (there was lots of room left). This power supply came with a voltage adjustment knob which I changed to 25V with no problem. This unit is only rated for 25W so as long as I dont go about plugging in an ADC monitor, I should be fine. After plugging it in, The LED now works.
I used the DVI connector to connect it to my monitor. I wanted to hook up 2 monitors, but the other connector was ADC. Well... as this is a different topic, I will write about it another time.