Looks like a burned phosphor from deflection failure before beam cutoff. Likely an intermittent problem causing horizontal, then vertical deflection failure leaving the beam concentrated in that small line. These sets do not have effective beam protect circuits. If I am correct, there is nothing you can do except replace the CRT, which will likely cost more than the set is worth. To be sure you need to look into the lens with a flashlight with the set off. If you see the line, it is damaged phosphor or some debris. The former is much more likely as any debris would cause diffusion at that level, not a distinct line.
This thread needs to be moved to the Akai forum in service & support.
