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I wouldn't bother checking the caps if you don't already have an ESR meter. The ESR can be unacceptable while they still measure spot on for capacitance. Before I got one I'd just replace any that looked suspicious (bulging, oozing) or were connected to anything else that looked suspicious (across the diodes that got hot).
Do all the supply rails come up? A bad sustain board can shut down the power supply. If Vs doesn't come up with the sustain board connected, but does come up with it disconnected the power supply is probably good. The main board will still shut it down when the set doesn't start up correctly.
If Vs (or VA) doesn't come up at all look for dry joints before replacing the board. I've fixed many Samsung plasma power supplies resoldering the FETs, driver transformers, diodes.
Disconnect the buffer board from the sustain board and power the set up. Check if Vscan (generated from Vs by a DC-DC converter on the sustain board) comes up.
Check the buffer board between Vscan and gnd with your meter on diode check. If it's not shorted it's probably ok. They can fail without shorting, but at least then they don't take out the sustain board.
If buffer board is shorted you can cut the Vscan traces to the buffer ICs to find and isolate the bad ones. Usually 1 or 2 will short, but the others are ok. With the shorted buffer ICs disconnected you can put it back in and you should get a partial picture if everything else is ok. The areas of the screen associated with the disconnected ICs should be completely dark.
If you see the blue line they mentioned at this point you've got a bad panel.
If buffer ICs that were ok immediately short you've got a short in the panel itself.
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