56" rear projection won't turn on

the three error code indicates that the Convergence ICs have failed, You will need to replace both STK392-110 ICs and possibly a couple of the 2.2 ohm 2watt resistors. You can get replacement ICs and resistors at the following link and they provide free installation instructions with pictures so you can do the repair yourself.
http://servicemanuals.vstore.ca/