It sounds like the SWR protection is keeping it shut down. If your jumper cable
and dummy load are all right then the problem must be between the final amp and
the RF connector. I have seen this problem on the rigs with the connector on
short pig tail from rig to save space. The center conductor breaks from the
flexing. if the connector is on the rig then check the wire from the circuit
board to plug. Last thought is a shorted Cap in the final matching section. Or
as you mentioned a faulty relay.

73 and good luck.
Don