Have you tried checking all the connections with a volt ohm meter?

Since you have a working specimen, if they are identical, try comparing them. Make sure none of the diodes have reverse bias, the resistors match ohms (this depends on their tolerance range), and the capacitors are within range.

It is not that complicated of a board, so use a paper clip affixed solid to a test probe on one end to check all the pins on the power connection, the electron gun pins, all the traces, and all the components.