Text preview for : 4-Control_Circuitry.pdf part of Mitsubishi VS-50805, WT-60805, WS-55905, WS-65905, WS-73905, WS-55805, WT-46805 Mitsubishi VS-50805, WT-60805, WS-55905, WS-65905, WS-73905, WS-55805, WT-46805 (Chassis V16 N W) (Training Manual + Schematic)

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Chapter 4 Control Circuit
The Control circuitry in the V16 chassis is necessarily complex. In addition to supporting the additional features included, communications for the optional Mitsubishi HD-1080 ATV Receiver are provided. This chapter will cover the following subjects: µPC Requirements I2C Bus Lines Control Interface Circuitry I/O Expander Parallel Inputs and Outputs AC Off Circuit Troubleshooting Tips

Block diagrams are provided to assist in servicing these circuits.

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From the Simplified Block Diagram in Figure 4-1, it is apparent that the Control Circuitry in the V16N and V16W chassis is similar to that in the VZ6 and V15 chassis. There are three I2C lines in the V16 chassis, used to: 1) Read and Write data to and from the E2PROM memory. 2) Control the Video, Sound and Deflection circuitry. 3) Control the Convergence circuitry

Control Circuit Overview

The Control Interface Circuitry: 1) Provides a communication link between the Main µPC and the Sub µPC. 2) Transfers data between the Main µPC and the Port Expander. 3) Directs Main µPC commands to the Line Doubling circuitry. 4) Is the interface between the Main µPC and, when used, an HD-1080 Advanced TV Receiver.

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Figure 4-2 illustrates the basic requirements for the Main and Sub µPCs operation. These are the same as in previous models: A 5 volt DC supply Ground Returns Timing Signals (Clock) Reset circuit to set the µPCs to their nominal point when power is initially applied to the set. The only difference between this circuit and that in the V15 chassis is there is no separate IC to perform the initial reset action. The Watchdog IC, IC709, performs this function in the V16. IC709 still monitors the circuits operation and activates a Reset pulse if one of the µPCs locks-up. During normal operation pulses from the Main Loop output of the Main µPC keep resetting the Watchdog IC so a reset pulse is not generated. If lock-up occurs, in either the Main or Sub µPC, no pulses are generated from the Main Loop output. IC709 responds by outputting a pulse to reset both µPCs.

µPC Basic Requirements

The logic at pin 42 of the Main µPC differs between the V16N and the V16W chassis. In the V16N chassis, R7A5 holds pin 42 LOW. There is no connection at pin 42 in the V16W.

Figure 4-3 shows the paths of the three I2C lines controlling the TV and the major ICs each line controls. The E2P line is dedicated to writing and reading data, to and from the E2PROM. This is mainly user programmed, and service adjustment data. The SDA1 line is also a dedicated line, used to control the Convergence Circuitry. The SDA2 line controls the rest of the TV, Video, Color, Sound, Deflection, etc. Although the Control circuitry is active, whether the TV is ON or OFF, the SDA2 line is only applied the PCB-YCS/ DECODER and PCB-PIP when the set is ON.

I2C Lines

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IC208 removes the SDA2 line from these PCBs when the set is OFF. Figure 4-4 illustrates a simplified drawing of the Control Interface. There are three ICs in the Interface circuitry: 1) IC703 serves as a buffer between the Main µPC and an external HD-1080 ATV Receiver. 2) IC721 directs data from the HD-1080 Receiver to IC720.

Control Interface Circuitry

3) IC720 directs data from the Sub µPC, PTC (Pulse Timing Control Doubler Circuit), I/O Expander and IC721 (HD1080 data) to the SB-IN input on the Main µPC. Since Main µPC SB-OUT and SB-IN lines are NOT I2C lines, chip select commands are required. 1) SB-CS selects the Sub µPC. 2) CS1 & CS2 selects the PTC circuitry. 3) IOX-CS selects the IN/OUT Expander 4) A-CS selects the HD-1080 Receiver (through IC703).

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Figure 4-5 shows the inputs and outputs of the I/O Port Expander, IC707. Besides Main µPC Data, Clock and Chip Select signals, there are four additional input ports. These are status inputs from the Tuner circuitry, denoting the current type of sound signals available from the Tuners. They inform the µPC whether the current signal is monaural or stereo, and if a SAP (Second Audio Program) signal is present. The outputs from IC707 are mainly signal selection commands: SW2 Selects either NTSC or SD/DVD as the main picture source. SW3 Selects the sub picture source, either NTSC or SD/DVD. SD/DVD Select the main picture sync signals, either NTSC or SD/DVD. M1, M2 and FMONO Select the type of sound from the Tuners. CLR-KLR prevents chroma signal output from the 3DYC Comb Filter.

I/O Port Expander

FR-SW removes any signal from the SD/ DVD sync circuit when Video Mute (blue raster) is activated. Signal from the SD/DVD Sync circuit is removed when the blue raster is activated to stabilize the onscreen display.

There are parallel single function Inputs and Outputs on both Main and Sub Microprocessors. In most cases, these are not new and have been used in the past. The V-Chip program blocking circuitry is internal to the µPCs. To decode the transmitted program rating requires a sample of the program's video signal. Main picture video is input to IC701 at pins 24 and 26, and sub picture video at pins 21 and 27. Also worth mentioning is the AC-OFF input at pin 9 of IC700. The input is not new, but the AC-OFF monitoring circuitry is different.

Parallel Inputs/Outputs

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Figure 4-6 illustrates the AC-Off circuitry. This circuit configuration differs from those on previous models. The purpose of the circuitry is same, to inform the Main µPC if power to the TV is lost. This allows the µPC to switch to a low current mode and store current operating data in the E2PROM memory before the backup supplies are lost. To sense a power loss, one side of the AC line is monitored. Diode D960 rectifies the signal from the AC line to drive the LED in PC901. The light from the LED drives the internal photo transistor into conduction, holding the base of Q702 LOW. The conduction of Q702 holds the AC-OFF line HIGH. When power is lost, the photo transistor in PC901 stops conducting, which cuts off Q702, removing the HIGH on the AC-OFF line. The logic change at pin 9 of IC700 informs the µPC that power has been lost. The LOW on the AC-OFF line, through IC720, also turns Q7X1 OFF. With Q7X1 OFF, the BLK2 line from IC721 goes HIGH, blanking all three CRTs.

AC-OFF Circuit

To check whether or not a µPC IC is functioning, check for pulses from the Main Loop output at pin 15. If no pulses are present, that µPC is not functioning. Even though there is no connection at pin 15 of the Sub µPC, the pulses should be present. If the set switches OFF and the Front Panel LED flashes three times, an automatic Reset was probably activated. If so, it may be due to a loss of communication between the Main and Sub µPCs, which activates the Watchdog circuitry. If the TV cannot be turned ON, it could be caused by the E2PROM IC704. To verify if this is the problem, remove or disable the E2PROM. To disable, connect a 100 Ohm resistor between the E2PROM Data or Clock line and ground. If the TV can now be switched ON, the E2PROM is probably at fault.

Troubleshooting Tips

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