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The ‘MainSupply’ line is the referencevoltage for the power supply. It is sampled by resistors
3543 and3544 and fed to the input of the regulator 7540 / 6540.This regulator drives the
feedback optocoupler 7515 to set the feedbackcontrol voltage on pin 3 of 7520.
The power supply in the set is ‘on’ anytime AC power goes to the set.
Derived Voltages
The voltages supplied by the secondary windingsof T5520 are:
z
‘MainAux’ forthe audio circuit (voltage depends on set execution, see table below),
z
3.3 V and 3.9 V for the microprocessor and
z
‘MainSupply’ for the horizontaloutput (voltage depends on set execution, see table
below).
Other supply voltages are provided by the LOT. It supplies +50 V(only for large screen sets),
+13 V, +8 V, +5V and a +200 V source for the video drive. The secondaryvoltages of the LOT
are monitored by the ‘EHTinformation’ lines.These lines are fed to the video processor part of
the UOC IC 7200on pins 11 and 34.
This circuit will shut ‘off’ the horizontaldrive in case of over-voltage or excessive beam current.
Pa
g
e 14 of 32SPMS
7/8/2004