Bridge CAD 256 free download

File name Bridge CAD256 service manual.pdf

Theory of Operation CAD-256 is a multisync color monitor. Its operation frequency horizontal is from 3OKHz to 64KHz and vertical is from 50Hz to 1OOHz. The circuitry are composited of 3 boards which are main board, switching mode power supply board and CRT board. Now detail the theory of operation in following paragraph. 1. The Main Board : The board contains horizontal deflection circuit vertical deflection circuit and signal processing circuit. A. Horizontal Deflection : The H. sync from pc or signal generator is input via R300 to IC U301 pin 16. IC U301 normalization the polarity of the sync. The output of the sync is negative polarity which is sent out from U301 pin 11.0300 is protecting diode for the IC U301. R329 and C317 is a high pass filter for the H. sync. The sync is fed through R329 and C317 to IC U301 pin 1. R330, R329 are bias resistors for the signal. IC U301 internally has two monostable multivibrator, their function is for H. phase control and AFC. The external RC of U301 pin 2 is for phase control. SVR304 is for 48KHz and SVR305A is for 64KHz, they are internal phase adjustment V/R. The R311, C320 in IC U303 pin 3 decide the time constant of pseudo H. sync generator for AFC circuit. Pin 4 of U303 is the input pin of flyback pulse from FBT for AFC circuit. C322 in IC pin 5 is the sawtooth generation capacitor for flyback pulse. In IC pin 6 C323 is the filter capacitor for AFC detector. The AFC output current is output at IC pin 7, through R334 to correct the oscillation frequency. The H. oscillator is a RC oscillator, R335 SVR306 and C326 decide the free running frequency. With the F to V voltage from IC U301 and U302 it can run multifrequency. R336 is the discharge capacitor for the oscillator. The output driver duty cycle is decided by the DC bias of pin 11 or by R341, R340, R393, Q320. The H. driver output is from pin 12 of IC U303. Q303 is the driver transistor which acts as a switch. During the time Q303 is driven on, energy is stored in the primary of T301. When Q303 off, energy is released through the secondary of T301 to drive the H. output transistor Q304. Q304 also acts as a switch. When Q304 is on, yoke current flows through L302, L303, C339 and yoke through Q304 to ground. During this period of time the scanning is from center of CRT to the right edge of CRT. Then Q304 is switched off, the scanning current reversed to charge the tuning capacitor C330, C337 which forms a tank circuit with the inductance of FBT and yoke. The time when the current of yoke from max. to zero the voltage on the capacitor is changed to max. This is called flyback. Durng this period of time the scanning is from the right edge back to the center of CRT. Then the trning capacitor is discharged through yoke until the yoke current reaches its negative max. It contributes the scanning from the center of CRT to the left edge of CRT. By the time yoke current wants to charge the tuning capacitor, damping diode conducts, the scanning current reduces