Tuner / Fip Power Supply (Ap Board) - Panasonic TC-26LX20 Technical Manual

Tuner / FIP Power Supply (AP Board)

The circuit below, located on the AP board, is the power source for the NTSC tuner and
the FIP. At power up, the 14Vdc created on the P board is applied to the collector of
Q808 via pin 4 of the transformer T802. Instantaneously, The SUB_ON output of the
microprocessor, converted into SUB_ACT, outputs a Low to the base of Q809 to turn it
off. As a result, the transistor Q808 turns on via the startup resistor R815. Current flow
through Q808 and the primary of the transformer causes a magnetic buildup in the
transformer. When the transistor reaches saturation and current stops to flow, the
output current at the other windings of the transformer is rectified into DC voltages that
are used by the tuner and the FIP. To restart the operation of the circuit, feedback
current is provided to Q808 via the capacitor C823 and resistor R820. Over-voltage
protection is provided when the –30Vdc of the FIP circuit exceeds the reverse
breakdown voltage of zener diode D811.
30-Volt Tuner Power Supply Circuit
Figure 14
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