A little while ago my daughter's ballet teacher gave me an old G4 Powerbook (A1001 model) as she had spilled a glass of orange juice on it which killed it for sure. Her brother had had a fiddle about and I could see there were some screws missing so I guess he'd probably made matters worse - if that was even possible.
Nevertheless, I thought I'd buy a new secondhand mobo off Ebay, and I got one for £20. Today I fitted it and remarkably it worked! Well, sort of, as I hadn't bargained that the HDD was also buggered to it won't boot rather it just hangs with the little folder with the question mark/face blinking away.
It's back to Ebay for a HDD then.