G4 Power Problem

I inherited a 2002 G4 Quicksilver (no discs), when I powered it up it went to desktop and then turned off.
I replaced the battery and the same thing - it runs for about a minute and a half. The led on motherboard goes out, I tried the small reset button to no avail. I have to remove power lead for around half an hour before it will power up to give me the minute and a bit - any less time unplugged means a shorter on time.

A friend suggested there might be some kind of thermal switch.

The fans all work.

As it has loads of bells and whistles and a lot of ram I would like to use it.

Help please

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From memory

This machine had capacitor issues (all boards and even at times in the power supply.) If you must get it working maybe find a working G4 off Ebay but no shop I know will touch these.

How are you are cap replacements?

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Imagine the results from this Google.

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