SONY BVF-55
Service Manual

2-3. Circuit Descriptions

Switching Power Supply Circuit (PS-241 Board) The +9.5 V constant voltage is generated by supplying the input voltage of 10.5 V dc through 17 V dc to the chopper regulator circuit. The IC301 controls the oscillation pulse width by feedbacking the chopper output voltage at the Q303 to the pin 2 and comparing it with the reference input voltage at the pin 1. This comparison output drives the Q303 after going through the Q301 and Q302. The output is then rectified by the following rectifiers to generate the dc voltage of +9.5 V dc. D302, L302, C307, and L303 C308, L304, C316, and C309 Tally Lamp Circuit (PS-241 Board) The Q308 and IC302 is a supply voltage variable circuit for the tally lamp PL501. The DIMMER control (1RV506) controls the output voltage level. (DC +12 V through 7 V) The luminance of the tally lamp is varied by the controlled output voltage level. The Q305 through Q307 turn the tally lamp PL501 ON and OFF. Setting the TALLY switch S501 to ON, the Q306 is turned off. The output voltage at the Q305 being added to the base of the Q307, the Q307 is turned ON and the tally lamp is lit. The R TALLY CONT signal from the R TALLY IN terminal (pin 4) of the CN501 connector is added to the base of the Q304 via the pin 3 of CN301. When the R TALLY CONT signal is high, the Q304 is turned on and the R TALLY LEDs (D502, D505/LP-59 board) are lit. The G TALLY CONT signal from the G TALLY IN terminal (pin 12) of the CN501 connector is added to the base of the Q309 via the pin 6 of CN301. When the G TALLY CONT signal is high, the Q309 is turned on and the G TALLY LEDs (D501, D504/LP-59 board) are lit.

BVF-55/55CE

2-5 (E)