Q: PPC G5 CRASHING SOON AFTER STARTUP.

Is this to help in testing PSU to see if it's alive or dead or to suggest a swap out of ATX supply in place of G5 PSU?

Would output readings be accurate enough if the PSU is not under load?

I have heard mention of LED's on the Logic board but never seen any indicator lights on mine. The only light is the white LED above the start button on the front of the case. This light flashes once when I press it for start and immediately dies after the double click sound (power relay I suppose). I looked for a red LED but couldn't see on. Where on the motherboard would it be if there were one?

The pinout is the long black "breadloaf" shaped connector behind the intake fans and plugging into the motherboard isn't it? Is that were I would check with the multi tester for trickle charge..

I found a powermac_g5.pdf" service manual online and used it's guidelines to test the PSU for trickle voltage. With the cable connector disconnected from the motherboard I tested voltage between pins #1 and #23. Voltage was 5.17. That's a good sign, but while looking around inside I discovered damage I did while heating the motherboard with the heat gun. Aaaaargh!!!

To achieve the 450˚ needed to reflow solder within the motherboard I got things hot enough to partially melt a couple of the connectors and to melt and fuse insulation in their wiring harnesses. This happened around the power jack for the front fans and the two connectors to the left of that jack.  It also partially melted plastic shoes for other components. I am guessing that melting and fusing the wiring harnesses lead to power shorts that may have done damage to other components. Also melted coverings for other connectors at the bottom of the motherboard. See attached images.

You don't need to ask me how stupid I feel. I am hoping this may save someone else from making similar mistakes. Apparently, the RAM slots can handle this high heat but some of the connectors and wiring around them can't. The success rate of heating the motherboard to heal solder micro cracks is good enough to recommend it as a last ditch effort, but obviously, some precautions need to be taken, Otherwise you can create new problems on top of old ones. 

I seem to have a working PSU but G5 doesn't startup so I now have to replace wiring connectors and who knows what else.

I think if I had foreseen the possibility and taken precaution to shield these elements, it would have been fine. It appears to have helped the motherboard before I added to the problems.

This saga gets even stranger as it goes along. I was ready to throw in the towel and called a dealer to purchase a refurrb G5. Nice lady asked about the history and fixes on my G5. She asked me to do one more thing before ordering the other computer. I tried her steps and to my astonishment, this fried and dead G5 booted up!!!

she had me disconnect the power cord, Take out PRAM battery, Hold PMU button for a count of ten, Hold the power button in for a count of 10, wait a half hour to allow capacitors to discharge. Then restart. I had taken these steps before but not quite in the same sequence. (prior to calling her, I had disconnected the fried connectors and capbles, but reconnected them for her test)

I started and restarted and used it for a day. worked perfectly.

Restarted it again today and grayscreens again. Several restarts to gray screen.

Restarted with CMD + V to see what it would say. once the text came up, it proceeded to boot all the way up. What gives?

In theory I can see that as a possibility. As a practicality how do I translate that to getting this G5 working?

Are we talking hardware or software or both?

To add some clues and possible credibility to this theory, I was having an progressively annoying problem before this computer went critical and I put out an SOS at the beginning of this thread: I use a Wacom Cintiq monitor with a stylus. Over the past few months on startup the USB powered stylus would sometimes work and sometimes not work. Keyboard and mouse still worked, but not the stylus. That's how I began to think USB port issues. Then, one day nothing USB worked or so I thought. Previous experience lead me to think it was a worsening USB issue, but, evidently it was a kernel panic and everything was frozen.  Next day, no video.

Possible culprit: lousy, degenerating capacitors.

I realize that I neglected to mention this mornings strange behavior. After a normal startup and using the computer for a while, I put on a youtube video and let the computer run under load. It was fine for a while then went through a cycle of shutting down spontaneously then immediately starting back up without missing it place in the video.  This happened every couple of minutes over a period of time before freezing. Evidently it was only a partial shutdown, like going to sleep (?) except prefs were set to not sleep hard drive or monitor.

Lots of symptoms and clues but no answers.

I have checked and reseated the video card a couple of times. This is a replacement video card.

The crazy-making part of this is how inconsistent and varied the problems are.

One day works great for hours, then spontaneously quits.

Another time only starts to gray screen time after time.