Hi. I have the same problem with my Hitachi P50S601. I have changed out the swollen caps but that didn't do the trick. Further troubleshooting, I have disconnected each and then both SDU boards, same flashing light issue. I disconnected the Y-SUS board, same issue. Then, disconnected X-SUS board, same issue. When I disconnected the logic board, the TV stayed on (but no picture). So, does this mean I just need to replace the logic board?
Have you tested the voltages to verify they are present at the levels on the tag on the panel? Be very careful to discharge the boards before reconnecting. It is easy to damage a board when reconnecting. Also, identify what you are disconnecting on both ends. For instance, dis you disconnect the logic board from the PS or another board?