Sony S75F Service Manual page 38

From U201 PIN10
OSC and output circuit: OSC is made up of C213 and PT201 and PUSH-PULL circuit is made up of Q209,
Q210. They are in alternate working state. R224, R225, R226, R227 are used for starting up OSC. The
voltage of Q209 and Q210 adds in PT201, and then it produces high voltage sine wave through LC
OSC. The high voltage of 1500V produced by PT201 is applied across the two terminals of backlight
through the effect of capacitance coupling. C215, C216, C232 are coupling capacitance for voltage
division as output. The two terminals of capacitance is applied across a certain voltage because of the
impedance exists in capacitor. The voltage across the backlight can decay to about 800V by selecting
the parameter value of capacitance.
Feedback circuit:Alternating voltage exists at the two terminals of R232 when the loads are working. After
being commuted and filtered, it changed to a DC sampling voltage. Apply the voltage to PIN14 of U201,
and it is used to control the duty of pulse output. The whole process acts as steadying the output voltage.
TO U201 PIN11
38
S75F Sony