Hitachi plasma- dark picture with figures highlighted in red

[Cornboats]

Hitachi 42PD4200

This sets has main board components supplied by LG.

I Can't get to the bottom of this one and its driving me nuts.

First Z-sus blew so I changed IPM.
Picture was ok but its ipm was running so hot it would have burnt out had I left it on for more than 5 minutes.

Second - Found 15v rail from y-sus was decreasing from switch on down to 9v.
This corresponded with the Z-sus ipm increase in temperature.

I changed the Y-sus board , got a good 15v rail and good picture.
Result-Yes .

It didn't last though. When I switched on again there is picture and sound but picture is very dark and figures are highlighted in red.

I looked up trouble shooting guide for inspiration and it says to check Y drive buffers. There are 2 testpoints near to the bottom drv outlet. Can'tmake out in guide wether these are for a diode check. Testing is infinite both ways anyway.

Could it be the buffers?

Oh and the 15 v rail is now down to 14V.