Think I've been sold a dead iPhone 3G... - Logic Boards?

Recently bought a iPhone for the missus that she was really happy with. It was a 2g iPhone that we got really cheap becuase the guy didnt know how to restore it.

I restored it - and it works - great.

I ended up then buying a 3g one for myself. The guy explained that it boots to the apple logo and you can get it to display the ITunes logo ready to sync.

What he didnt say is it will only do this on mains power. Once you remove the power cable it instantly dies.

First I thought battery, but no - it doesnt show the charge logo so it cant be a poor battery not holding charge can it? otherwise it would have the red battery logo all the time surely?

so I decided it must be the charging dock.

I ordered the parts, they arrived and I replaced the dock. interestingly enough - while i was inside I noticed the water labels had been tripped on both the dock and the lower part of the logic board. (oh ****).

ever the optimistic, I replaced - cleaned what I could with nail polish remover and rebuilt. I also checked for volts across the PCB battery terminals - which indicated 1.5v. - so I assume the battery has charge?

long story short - (or not) I'm not fixed.

still does the same think and im more ££ down.

your thoughts? new logic board? - does anyone know where I can get them cheap?

should I cut my losses?

no other water sensors are tripped - i.e. top PCB / headphone jack and so on.

tell me its not dead!!!!!