Hitachi CM721FET, Руководство по обслуживанию

Страница: 18 / 37

-- 17 -
G. Horizontal Drive
The drive pulse output from pin 7 of U401 (TDA 4855) through a buffer (Q416/ Q417) and drive stage
(Q503, T501), drives the HOR. Output transistor (Q504).
G-1. CS Circuit
CS control is multiple type the SW1/ SW2/ SW3/ SW5 of U1 to control Q512/ Q520/
Q514/Q515
CS transistor switch Ref. To Fig. Below-
G-2. HORIZONTAL Linear
The D-C HOR. linear control circuit outputs a duty cycle (PWM) through Q545 & Q546 to
the winding of L501 to ADJ. the inductance of linear coil of L501.
G-3. HV circuit
A reference voltage is derived from the bleeder of FBT and input to U801 (PWM modulator IC)
to drive Q801.
When Q801 turns on the energy is stored in the FBT. When Q801 turns off, the resonate circuit
creates a pulse to the FBT to generate a HV (*25KV / 26KV) and G5 voltage (6.1~7.8KV) and
G1 voltage (-180V) and +32V for X-RAY protection and +300V for dynamic focus.
H. Video Amp Circuit
H-1. Video PRE AMP
U301 (M52743) is the Video PRE-AMP. The input signal is 0.7Vp-p, the pre-amp IC U301
amplifies the video signal to be 3-4 Vp-p and controls white balance and contrast.
H-2. Video output AMP
This stage including AMP IC (U303) amplifies the video signal to be around 40Vp-p and
drives the CRT cathode.
H-3. OSD signal
The Mirco-p output DATA and CLK, to the OSD IC U302 (CM46542) and output data on
the VIDEO OUTPUT.