I have a Panasonic Tx-28DK1 TV (Euro4 chassis).

when attempting to switch on, the standby LED switches from red to
green, but after about 4 secs a relay clicks and it reverts to standby.

Before the fault became permanent, it was intermittent - would
eventually switch after several attempts.

The Line Output Transistor had gone low resistance between base and
emitter (22ohms both ways), but replacing it didn't fix the problem. I
have removed and checked all the large high voltage electrolytics for
value and leakage at up to 50Vdc on a bench PSU, but they're all OK.

Any ideas where I might look next?

Tony

PS. Does anyone have a complete schematic they'd be prepared to share? I
bought a manual online, but it's obviously dodgy because the (badly)
scanned schematics are very incomplete. The parts list is complete though.