With no picture but only sound on my Akai PDP 4294

Try replacing the Y-sustain board. Might have to replace buffers attached to it too. Have you had it diagnosed? My picture went out and I replaced the power supply board. Worked for 2 weeks then acted up again. Got a different power supply board. Same thing 2 weeks later. Was told it now was a bad Y-sustain board. Replaced y-sustain board. Worked OK for about 2 hours then started having picture issues. Not the same issues before power supply or y-sustain problem. Was told that you might have to replace buffers attached to y-sustain when you replace y-sustain. Tired of dealing with it and only watch a couple hours a day, so I don't always have the problem unless I watch the TV for a long time. Will eventually replace buffers to see if that works. I would definitely find a place that gives free estimates or close to free to get a technician diagnosis. Then you can decide if you are able to do the work yourself.