As far as i know DCB board is always OK (never seen one bad) unfortunately PAV board is the culprit usually.

I have collected 5 Imac G3's so far ... and 3 of them were gone.

You cant test the logic board (the service manual is really well done here)

When you wrote nothing... is nothing at all (no Led...) ?

The FBT is probably bad... but i don't know if a substitute is available.