Panasonic TH-37PX50U Technical Manual page 25

The SU and SD boards are demultiplexer boards that are responsible for converting
serial data output of the SC board into parallel data to drive the panel.
The SS board is responsible for the generation of the sustain pulses. Sustain pulses are
used to initialize and control the brightness of the screen.
The SS2 and SS3 boards are extension (connector) boards used to connect the SC
board to the panel.
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