Assessments - 2, GPA: 4
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Regulation Regulation is achieved by monitoring the 110V secondary supply, and through IC9A51 and PC9A50 a correction voltage is fed back to pin 1 of IC9A50. The voltage at pin 1 determines the PWM (duty cycle) of 3-8 the oscillator drive to the FET. The PWM is automatically changed to maintain a constant 110V source. Five supplies are directly generated by signal from T9A50, 210V, 110V, 17V, +24V and -24V. Power Distributions Figure 3-10 shows the Switched Supplies Power Distribution. The 110V supplies power to DBF, Horizontal Drive, HV and SVM circuitry. The +24 source supplies power to the Vertical Output, X-Protect and Convergence circuitry. It also generates the 12V-MAIN supply that is dedicated to HV Drive and Deflection Loss circuitry. The -24V supply is used in the Convergence circuitry, and is the source for the -20V supply used in the CRT Drive circuitry. The 210V supply is also used in the CRT Drive circuits. Troubleshooting The most common symptom due to Power Supply problems is "The TV Will Not Turn On". The Flow Chart in Figure 3-11 may be of some help in isolating the cause of a "Won't Turn On Problem". If the LED flashes: • For 1 minute before the TV turns On: This is normal, it takes about 1 minute for the circuitry to Boot Up. Boot Up occurs the first time the TV is plugged, and if in the Low Energy mode when the Power button is pressed. • Flashes Continuously It indicates the TV .PC is not functioning. • Flashes-Stops-Flashes-Stops-etc. It indicates a loss of communication between the TV .PC and the DM .PC. 3-9 If the LED does not flash: • Check that the DM board is seated properly. • Check that there is Standby 9VS (Fig. 3-2). • Check that the SUB-POWER command line does not go High (Fig. 3-5). • Chirping sound - check the Standby Regulator, IC9A20 (Fig.3-5). • If it Turns On then Off -Check the ±24V fuses -Check Horizontal Deflection Circuitry. 3-10 Chapter 4 Control Circuitry As in the two earlier integrated HDTV chassis, V19 and V21, the V23 uses two Microprocessors in the Control circuitry. 1) TV .PC … controlling the analog circuitry. 2) DM .PC … controlling the digital circuitry. The two .PCs constantly communicate with each other. User commands are input to the TV .PC. Digital commands are forwarded from the TV .PC to the DM .PC. The TV .PC generates Control commands from two sources.: 1) User commands from the front panel or remote control 2) Commands from the DM .PC. Even though circuitry is becoming more complex, the same basic requirements must be met for a .PC to operate. Basic .PC Requirements Figure 4-1 illustrates the four basic requirements for the TV .PC operation in the V23. 1) DC Supply … 3.3V-ES and 5VS. 2) Ground Returns … pins 8, 9 and 14. 3) Timing Signal … 15 mHz Clock Oscillator 4) Reset circuitry … sets the .PC to its nominal starting point There is similar circuitry for the DM .PC. Since the DM Module is considered a replaceable component 4-1 4-2 we are not showing the details of the DM circuitry. Figure 4-1 shows only the DC supplies and Reset signal going to the DM module. Reset Circuitry Figure 4-2 illustrates the Reset circuitry in more detail. The normal and Reset logic are shown in the diagram. IC7C70 is the Reset IC. A Low from pin 1 resets the TV .PC. IC7C70 is a Watch Dog type of Reset IC that monitors the .PC’s operation. It has an internal counter that is continually reset by pulses from the .PC, input at pin 4 of the IC. If the .PC locks up, no pulses are generated. The counter reaches its maximum count and a reset pulse is output at pin 1 to reset the .PC. 4-3 Both the .PCs have the ability to reset each other if communication is lost. IC7C30 serves as a Reset interface between the two .PCs and the front panel Reset button. If the TV .PC gets no response from the DM, it outputs a High at pin 73 of IC7A00. The High is routed through IC7C30 and drives the DM-RESET input at pin 15 of the TC connector High. Conversely, if the DM .PC gets no response from IC7A00, the DM outputs a Low at pin 18 of the VC connector. The Low, through IC7C30 activates a TV Reset pulse from IC7C70. When the front panel recessed Reset button is pressed, both .PCs are reset through IC7C30. IC7A00 also outputs reset pulses for the Convergence Generator, Audio Control, 3DYC and MLink circuitry. Input Command Circuitry Figure 4-3 illustrates the Command Input circuit. It is basically the same as that in the V19 and V21 so an in depth description is only necessary on those parts that are different. The front panel Buttons are in a conventional resistive ladder configuration. Pressing a button changes the voltage at the KSC0 or KSC1 input of the .PC. The command is identified by the change in voltage at the KSC input. There are differences in the Remote input circuitry due to the Remote Learning feature of the V23. As in previous models there are two Remote Preamps: 1) A conventional Mitsubishi Preamp. 2) A wideband Preamp amplifying the IR signals of most manufacturers. 4-4 IR sig...
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