I have 3 280 motherboards all washed and recapped as well as a 270c.  I will tell you my 270 will not boot by itself but will boot in the dock.  all the 280 won't even power on.  Its the strangest thing I have seen to date, as clean as the boards are, for them not to work is stranger than the 3400c.  At least pram battery leakage made sense in the 3400.

Sounds like the power supply on the dock is weak and/or the ejection motor is seized.