Quicksilver shutdown problems

Hello Skorpan
I also have a Quicksilver & Gigabit Ethernet that have had similar problems.
It sounds like its probably bad or incompatible RAM module(s), so just call the used computer stores that are around you locally find who has the best prices on PC133 modules but before you buy them ask them to test them to make sure they're working. (Make sure they are 64-bit wide 128-Mbit technology 3.3v unbuffered non ecc 168-pin PC 133 MHz SDRAM DIMMs (chips on both side) Modules it will accept upto three 512 MB so 1.5 GB total)
If the RAM swap doesn't work something else also worth noting is that a common problem isn't the whole Power Supply going bad but only the part that supplies ADC (Apple Display Connector) power but that only applies to you if you're using a Apple ADC monitor (one cable design just plugs into tower no extra power cable for the monitor) if you're using a ADC monitor just try plugging the tower into a standard VGA monitor & I'd be willing to bet money that that'd fix your flaky power problem.
But if that still doesn't fix the problem here's what you do to test the power supply:
Lay the computer on a wood, tile or other non carpet or non metallic space.
Pull the handle on the side of the tower & open up the side of the case.
Then remove the 4 pin cables from all the drives.
Then remove the 22 pin cable from the Logic Board.
Then remove 4 pin cable from the Logic Board.
Then unplug the power cable from the internal case fan.
Then take the PATA cables off of your CD/DVD & Zip Drive.
Then unscrew the three internal philips screws holding the drives bracket in place.
Then pull out the drives.
Then unscrew the internal philips screw on the little L bracket on the back side of the power supply holding it in place.
Then get a allen wrench I forget which size but it is a smaller one then unscrew the three torx screws on the external backside of the case that are holding the power supply in place.
Then gently pull the Power Supply wiring harness up & out of the hole in the middle of the case behind the back side of the power supply on the inside of the case.
Then unseat the power supply with its freed wiring harness & pull it out of the case.
Then ground yourself by touching a unpainted pci card bracket on the case with each hand one at a time.
Then plug in the power supply & use the Volt Meter to test each pin one at a time starting with pin 1.
Here's what the voltage on each pin of a good Power Supply should be:
On the 22 pin adapter: (pin one is on the bottom right side where the outside of the adapter is smooth , pin 12 starts on the right at the top the side that has the locking notch on the outside.
Pin 1+3.3v Pin 2 +3.3v Pin 3 Ground 0v Pin 4 +5v Pin 5 Ground 0v Pin 6 +5v Pin 7 Ground 0v Pin 8 +3.3v Pin 9 +25v Pin 10 +12v Pin 11 Ground 0v Pin 12 +3.3v Pin 13 -12v Pin 14 Ground 0v Pin 15 Power On 0v Pin 16 Ground 0v Pin 17 Ground 0v Pin 18 Ground 0v Pin 19 Ground 0v Pin 20 +5v Pin 21 +5v Pin 22 +22v Trickle Charge
And on the 4 pin adapter: Pin 1 is on bottom right side & pin 3 on top right side.
Pin 1 +12v Pin 2 +12v Pin 3 0v Pin 4 0v
And thats all there is to it.
Well I hope this helps.
Yours Truly: A fellow Mac Head
Have a good day, take care.

You don't need to remove the power supply to check the voltages. Here's a diagram showing the power supply's connector pins & voltages on the logic board connector. http://atxg4.com/quicksilver.html

When the Mac is running, open the side door & you should see a red LED somewhere on the logic board. This is a power indicator. When it shuts down, is the LED Off?

 Cheers, Tom 😉

Hello Skorpan
With what you said in your reply it sounds like its either the Processor or Power Supply.
But there's no way to really test the Processor other than to power on the tower but if the Processor isn't heating up as you said it sounds like it could very well be bad probably due to a crack in the outer ceramic casing or a bad interconnect in the silicon die.
But its also a worthwhile endeavor to test the voltages of the power supply, to do that just read the step by step instructions in my previous post.
If the voltages aren't correct then it might just be a bad fuse or capacitor inside the Power Supply you can open that up (but only do so after its been unplugged & turned off for a couple days to make sure its totally discharged (also make sure to ground yourself on unpainted metal before working inside the Power Supply)) if there are any bulging or leaky capacitors inside the Power Supply & you have soldering knowledge you can easily & cheaply replace those &/or replace the internal fuse if its bad also very cheaply.
If its the processor & its a OWC upgrade it might still be under warranty & you might be able to get it replaced for free or fairly affordably., If its the Power Supply you can buy a new or used one on say ebay or craigslist., Or you could buy another identical machine & swap out the Power Supplies which would probably be cheaper another identical machine would only set you back about $20 to $100 whereas just the Power Supply would run you anywhere between $25 to $500 depending on where you buy it from & if you buy it used or new.
Well I hope this helps & best of luck.
Yours Truly: A fellow Mac Head
Have a good weekend, take care.

1-After taking the PSU out of the mac, it needs to be connected to the logic board with the power on?

Leave the PSU in the tower, and leave the connector connected to the logic board.

2-I assume that within the PSU (atfer opening) are the connectors, I need to check? not the the connectors attached to the logic board?

You are testing the electrical output AT the logic board connector.
For all to work correctly, the connector MUST stay connected to the logic board.
Inserting a probe along side each wire down to the connector pin in the plastic connector will allow you to achieve readings.

All the black wires will be interconnected grounds. All wires of an identical color will have identical Voltages. There is no need to remove the Power supply to test it.

There must be an "always-on" power supply available to start up. It will be present even when the power is nominally off, provided the AC power cord is plugged in. In many Macs such as the Quicksilver that provide 25 Volt power to the AGP slot, 25 Volts is used as the "always-on" Voltage.

After your Mac is powered on, you can also check for +12 Volts and +5 Volts at any Hard drive power connector. This may be easier than jamming the probes into the back of the main DC power connector.

To make additional progress after determining your power supply is good, you will need more known-good components, such as a spare processor or spare motherboard. Swapping components between your multiple Macs MAY change the symptoms, which could provide additional insights,