[robespierre]

If the design is anything like the FW900 and other late Sony displays, there is a separate transistor for the horizontal drive (which goes to the yoke) and the HV oscillator (which goes to the flyback transformer).
In the FW900 schematic, those are Q515 (a 2SC5570) and Q901/Q906 (two 2SK2655's) respectively. The H Drive transistor is on the long heatsink along the edge of the board, while the HV FETs are near the FBT (which is opposite to the long heatsink), and have their own small heatsinks.