Had a Nanao MS-2934 that was slowly losing the green color and eventually lost green entirely. Pulled the transistors C4001on the neck board and they all tested good out of circuit. Rotated between the colors anyway. No change as expected. Tested zener diode ZD311 on-board that was feeding the green transistor and it flowed current both ways. Also had a spark gap ampoule bulb that was busted on the neck board. Replaced both from another dead MS-2934. All working now.