Acer AC501 AC501 Monitor Service Guide - Page 18

I-4. Horizontal Driver Circuit The driver pulse that come from U401 pin7 drive Q506,then transfomer T501 convert driver pulse to driver current to drive horizontal output transistor Q801. I-5. Horizontal Output Stage There is different Cs value in different horizontal frequency. Hf Cs Hf < 40K C805 + C804 + C814 Hf < 58.5K C804 + C805 Hf > 58.5K C804 I-6. Flyback Transformer In the primary of F, B, T, there is about 1103Vpp in the LC resonant interval, it convert to the secondary of F.B.T to produce about 24.7KV for CRT anode voltage. The other bias for CRT is G4 (4~8KV), G2 (0~1000V) and G1 (-160V). J. Video AMP. Circuit J-1. Video PRE. AMP. The video pre-amp IC is U301 (KA2143B). The input signal is 0.7Vpp, then pre-amp IC U301 amplify the video signal to 4~5Vp. The WHITE BALANCE and CONTRAST shall be adjusted by adjustment the bias voltage of U301. Fig. 5 is the block diagram. J-2. Video AMPLIFIER The video amplifier is U303 (LM2439), it amplify video signal to about 40Vpp. Video output signal add to cathode by AC coupling. The DC bias is controlled by the output pwm of IC U302. J-1. Video PRE. AMP. The video pre-amp IC is U301(KA2143B). The input signal is 0.7Vpp, then pre-amp IC U301 amplify the video signal to 4~5Vpp. The WHITE BALANCE and CONTRAST shall be adjusted by adjustment the bias voltage of U301. Fig. 5 is the block diagram. J-2. Video AMPLIFIER The video amplifier is U303 (LM2439), it amplify video signal to about 40Vpp. Video output signal add to cathode by AC coupling. The DC bias is controlled by the output pwm of IC U302. 18