[JohnCT]

I'll never say never, but I don't think there's a way you can kill a flyback unless you intentionally wired it to fail. There were a few instances of extreme HV runaway if a shutdown circuit was bypassed or if a retrace capacitor suddenly opened that could damage a fly, but these were in color TVs.

Going on the assumption that this Sony TV uses an actual flyback as opposed to a separate HV transformer and a horiz deflection transformer, the fact you had a vertical line means the HV was there, so the horiz osc was running.

Before you do anything else, verify the resistance of the horiz yoke windings, and then check to see they're properly connected to the board. Also, look for a capacitor that couples the yoke to the fly. If the yoke is open or not loading the fly, it will cause problems for the HV section.

My guess is that the horiz output transistor failed (again, assuming a flyback setup).

Is there a schematic we can see?

John