Sharp FO-2970M Service Manual - Page 47

d. High voltage unit control The high voltage unit outputs the following voltages: • Main charger voltage (DC-950V + AC600V peak to peak) • Transfer charger voltage (DC+2100V + AC600V peak to peak) • Developing bias voltage (DC-390V) The following signals are outputted from the CPU (ASIC) to control the above voltages. • MCON This signal is to turn on/off the main charger. When this signal is outputted, Q7 is driven to the high impedance state. Then Q9 conducts to drive transformer T2. As a result, the main charger voltage is outputted to the secondary side of the transformer. • TC/BIASON This signal is to turn on/off the transfer charger and the developing bias voltage. When this signal is outputted, Q3 is driven to the high impedance state. Then Q5 is conducted to drive T1 to output the transfer charger voltage and developing bias voltage to the secondary side of the transformer. • PWMSIN This signal is to control the main charger voltage and the transfer charger voltage. The PWM pulse of 295.28Hz is outputted. This pulse waveform adds the AC component to the main charger voltage and the transfer charger voltage. By changing the pulse duty of this signal, the main charger voltage and the transfer charger voltage are controlled (during temperature correction operation). When the pulse duty of this signal is changed, the collector currents of Q4 and Q8 are changed. Therefore, the base current of Q9 and the drive current of transformer T2 are changed to change the main charger voltage and the transfer charger voltage. R29, R31, C19, and C20 from a filter circuit which dulls the waveform of PWMSIN signal. e. Electrical connection CONTROL PWB PRINTER PWB ASIC IC15 (LR38784A) 131 MC ON 5 12 Q7 Driver IC1 129 TC/Bias ON 3 14 Q3 Q9 Q8 +24VP T2 Transformer +24VP Q5 T1 Transformer Q6 CPU (SH7041) 115 PW MSIN Q4 CNPRT Fig. 8 5 - 11 FO-2970MU Charger roller MC OPC DRUM Separation electrode TC DC 100V Bias Transfer roller Doctor Developing roller Supply roliler