Text preview for : 5-Signal_Processing.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 5 Video-Color Signal Processing
As discussed in the introduction, there are two types of V16 chassis, the V16N and the V16W. The most apparent difference between the two chassis is the aspect ratio. V16N models have a 4:3 screen, and V16W models use a 16:9 screen. Less obvious are the differences in PIP/POP and Format features. These differences are more evident when the VideoColor signal path is analyzed. In addition, both V16 chassis are capable of producing High Definition, 1080i as well as Standard Definition, 480p and 480i pictures when used with an Advanced TV Receiver. They will also produce pictures from DVD, 480p and 480i signals. These details make the Video-Color Signal Processing circuitry far more complex than a standard NTSC receiver. This chapter will cover: Video/Color Signal Path Signal Processing by PCB As in previous chapters, block diagrams are provided to help streamline circuit analysis and troubleshooting techniques.

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Figure 5-1 illustrates an Overall Block Diagram of the Video/Color circuitry. Although not indicated in the diagram, the PCB-SIGNAL serves as an interface between most of the PCBs. The terminology YUV is used in Figure 5-1 to denote signals. Remember Y is luminance, U is Cb (B-Y) and V is Cr (R-Y). There are two different PCB-PIPs, one for the V16N and one for the V16W. The V16N PIP circuit is basically the same as in previous chassis, except the Main Picture Y signal is enhanced in IC6V30 before the PIP picture is inserted. The V16W PIP circuitry is similar to that in the V15 except for two additions. The Main Y signal is enhanced in IC7310 before the PIP picture is inserted. Also, a Scalar Bypass IC, IC7300, has been added.

Overall Video/Color Signal Path

This IC bypasses the Main Scalar circuit when using an External Input in the Expanded mode. The Line Doubling Circuitry is basically the same as that in the VZ6 and V15 chassis. The resulting YUV signals, at twice the horizontal scan rate, pass through enhancement circuitry in IC2D00 and are applied to IC2B00, the Multi-Component Processor. The signals are then converted to a RGB format and directed to the CRTs. As in the previous chassis, the SDTV, or HDTV, signals are applied to IC2B00. In the V16 chassis, the DVD input signals are also applied to IC2B00. IC2B00 selects either SDTV or DVD 480i signals and directs them to the Main and Sub Signal Select circuitry on the PCB-SIGNAL. IC2B00 can only select one of the two signals. If one of these signals is the main picture source, the other signal is not available as the sub picture source.

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If the selected main picture signal is 1080i HDTV, 480p SDTV or 480p DVD, the signals are converted to RGB in IC2B00 and directed to the CRTs. Since the HDTV and 480p format signals are not directed through the PIP and Doubler circuitry, the Expansion and PIP features are not valid. IC2B00 will accept signals from the ATV inputs in either the RGB or Component (Y, Pr and Pb) formats. The default is the Component signal format. When a Mitsubishi HD-1080 Receiver is connected to the TV, it automatically switches to the RGB format.

The signal processing PCBs are double sided, except the PCB-DOUBLER which has four layers. Due to difficult accessibility and circuit density, some failures will require replacement of the PCB rather than repair. However, the PCB-SIGNAL will generally require troubleshooting to the component level. Figure 5-2 shows the Video/Color circuitry interconnections between the various PCBs. Checking for the presence of signal(s) at the various connector pins helps isolate a problem to a specific PCB.

PCB Interface

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The Video/Color circuitry is located on six PCBs, the PCB-SIGNAL and five plug in PCBs. The following describes the major Video/Color circuitry on each of the PCBs. PCB-SIGNAL Tuner and Control circuitry Main Picture NTSC/DVD/SDTV Signal Select circuitry Sub Picture NTSC/SDTV Signal Select circuitry Serves as an inter-face between the five plug in PCBs. PCB-TERMINAL The rear External Inputs and Outputs The NTSC Signal Select circuitry (AV Switch) Audio signal processing

Video/Color PCB Functions

PCB-YCS/DECODER Main and Sub Y/C Separation circuitry Main and Sub Matrix (Chroma demodulation and matrix to Y-Cb-Cr) PCB-PIP Sub Picture PIP Processing PIP Insertion circuitry Scalar (V16W) PCB-DOUBLER Signal A/D Conversion Line Doubling circuit Signal D/A Conversion PCB-RGB Y Signal Enhancement (aperture) Main Signal Matrix (Y, Cb, Cr to RGB) HDI Signal Matrix (RGB to Y, Cb, Cr) Block diagrams and circuit descriptions of the signal processing circuitry on each PCB will be provided next.

NOTES: __________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________

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The Tuning circuitry, located on the PCB-SIGNAL, is similar to previous models except the Sub Tuner outputs Left and Right Audio Channels for the Sub Audio Output Jacks (V16W only). Figure 5-3 illustrates a simplified circuit diagram of the Tuning Circuitry. Both Tuners contain the following circuitry: Tuner circuitry Video/Sound I.F., and Demodulator circuitry Sound MCS Decoders (V16N-- 1 only) Both Tuners are controlled by the SDA2 and SCL2 lines from the Control circuitry. The Tuners generate Status Signals, informing the Control circuitry of their current status. The Status Signals, and their purpose, are listed below:

Tuning Circuitry

AGC Indicates current signal strength, required for the Auto Picture feature. AFT Indicates when a channel is properly tuned. ST LED Indicates that the current sound signal is stereo. SAP LED Indicates if a SAP signal is being received. Two addition Status Signals are derived from Sync Separator circuitry, SD1 and SD2. The presence of sync informs the Control Circuitry that signal is present when a channel change is activated. The logic on the M1, M2 and FMONO lines selects the sound signal output from the Tuner, either Monaural, Stereo or SAP.

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The rear External Inputs and Outputs, and the NTSC Signal Select circuitry are located on the PCB-TERMINAL, Figure 5-4. Not shown are four sets of External Input Jacks, EXT 1 through 4. External Inputs 1, 2 and 3 are on the rear of the set. External-4 is on the sets front panel. In addition, DVD Component Input Jacks (Y, Cb and Cr) are also located on the rear of the set. With no cables connected to the DVD Jacks, the DVD selection option does not appear on-screen. When cables are connected to the DVD Jacks, the DVD selection replaces the External-3 option. The signals from the DVD Inputs are directed to Buffer circuitry and then to the PCB-RGB. Part of the DVD-Y signal is also directed to pin 30 of IC7600, and is output as the MainY signal at pin 44 of the IC. This prevents Video Muting from being activated. The SD3 (Sync Detector 3) circuitry at pin 44 informs the Control Circuitry that signal is present. If there is no signal detected, the screen will be automatically muted. NTSC Signal Selection Signal selection is controlled by the SDA2 and SCL2 I2C lines from the Control Circuitry. SDA2


is input at pin 34, and SCL2 at pin 33 of IC7600. The selected Video/Color signals output from the IC are: MAIN-Y (S-Video) or MAIN-V at pin 44. MAIN-C (S-Video) at pin 47. SUB-V at pin 53. Main Composite at pin 41, for the Video Output Jack. The operation of IC7600 is basically the same as AV Switch circuitry in previous models, so an in depth description is not required.

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Next the Main and Sub Video signals are processed by circuitry located on the PCB-YCS/DECODER as shown in Figure 5-5. The selected Main signal can be composite video, or, if an S-Video Input is being used, separate Y and C. The Main Video, or separate Y signal, is directed from PCB-SIGNAL to pin 20 of connector GE. The separate C signal is input to pin 22 of GE. When the input signal is composite video, it is directed to pin 70 of IC2000, a 3-D Y/C Comb Filter. IC2000 separates the Y and C components of the signal. If the input signal is S-Video, the already separate Y and C signals are selected by the switches internal to IC2150 and IC2160, bypass-


ing the comb filter. These ICs are controlled by the Y/C-SW line from the Control Circuitry. The Y signal is applied to pin 34 of IC2200. The C signal is applied to pin 32 of IC2200. IC 2200 performs two functions. 1) The chrominance signal is demodulated to the color difference R-Y and B-Y signals. 2) The luminance and color difference signals are matrixed to the YUV (Y, Cb, Cr) format. The Sub Composite Video signal is applied to pin 34 of IC2301. Internal Frequency Filters separate the Y and C signals. The C signal is demodulated and an internal Matrix circuit generates U(Cb) and V(Cr) signals. The Sub YUV signals from the IC are directed to the PCB-SIGNAL.

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Figure 5-6 illustrates the Video/Color circuitry located on the PCB-SIGNAL between the PCB-YCS-DECODER and the PCB-PIP. The circuitry selects one of the following for the Main signal: NTSC source signals from the PCB-YCS/DECODER. 480i DVD or SDTV signals from the PCB-RGB. IC2A3 selects NTSC, or SD/DVD signals as the Main picture source. IC2A1 selects the Sub signals, either the NTSC Sub signals from the PCB-YCS/ DECODER, or SD/DVD signals. The selected Main and Sub signals are directed to the circuitry on the PCB-PIP.


NOTES: __________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________

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The V16 uses two different PCB-PIPs, a basic one for the V16N and a more advanced one for the V16W. V16N PIP Figure 5-7 illustrates the PIP circuitry in the V16N chassis. IC6P00 is the same PIP IC that has been used in several previous PTV chassis. It converts Sub Picture signals to digital and writes them into memory. The memory is then read at a rate to pro-

duce the small PIP insert picture. The signals are converted back to analog and directed to the PIP insertion circuit. IC6P50 inserts the PIP picture in the Main Picture signal. Timing for PIP insertion is provided by the SEL signal from pin 12 of IC6P00. Note that prior to PIP insertion, the Main Y signal is enhanced by IC6V30.

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V16W PIP In Figure 5-8 the PIP circuitry in the V16W chassis is shown. The circuitry in this version is far more involved to provide for the additional POP and Format features used on the 16:9 wide screen. The Main and Sub picture signals are applied to the scaling circuitry in IC7000 and IC7001 respectively. The Scalars convert the signals to digital and write them into memory. The memory is then read at a rate to produce appropriately proportioned pictures for the mode selected. The signals are converted

back to analog and directed to the PIP insertion circuit, IC7330. IC7330 combines the two sets of signals together to develope the complete picture output. While viewing an External Input in the Expanded mode, IC 7300 switches the main picture signals to bypass the scaling process. Like the V16N, the V16W PIP circuit provides enhancement for the luminance signal. This function is performed by IC7310.

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The circuitry on the PCB-DOUBLER doubles the number of lines comprising the picture. To double the number of lines, two adjacent horizontal lines are compared and through an interpolation process an additional line is generated. Of course, with line doubling the horizontal frequency doubles, from 15.75 KHZ to 31.5 KHZ. To perform the line interpolation process, the signals must be converted from analog to digital. The line comparison, and new line generation occur while the signals are in a digital format. Then the signals must be converted back to analog signals to drive the CRTs. Figure 5-9 illustrates the Line Doubling circuitry in the V16. The input Y signal is converted to an 8 bit digital signal by IC7D01. The signal is then written into memory. There are three Y signal Field Memories, IC7H01, IC7D07 and IC7D08. Since interlace scanning is used, adjacent lines are actually in adjacent fields. Therefore, three Field Memories are required. Since the eye is less sensitive to color, less color information is required. IC7H00 alternately selects samples of the Cr and Cb signals. The signals are converted to digital by IC7D03, and written into Field Memory IC7H02. Due to less color data, only one Field Memory is required.


Data is then read from memory and the interpolation process occurs in IC7D04, the Scan Line Processor. The outputs of IC7D04 are written into memory. Y signal data is stored in IC7G02, and Color signal data in IC7G03. The data is read from memory in the sequence to produce the 960 line picture. Two D-Type Flip Flops, IC7G04 and IC7G05, separate the Cb and Cr data. All three digital signals, Y, Cb and Cr, are applied to IC7G01, a 3 Channel Digital/Analog Converter. The outputs of the IC are the Y, Cb and Cr analog signals at a 31.5 KHZ horizontal rate. The Doubler circuitry is controlled by IC7D0, the PTC-Logic Control IC. PTC stands for Pulse Timing Control. IC7D0 generates all the Control and Timing Signals for the doubling operation, including the Control Signals for the D/A and A/D Converters. The TVs Control Circuitry controls IC7D0 through the SB-OUT, SB-IN and SB-CLOCK lines. These are the same lines used for Main and Sub uPC intercommunication, and for controlling an External HD1080 Receiver. In addition, two Chip Select lines are used to control the PTC Logic circuit, CS1 and CS2 from the Control Circuitry.

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The signals from the PCB-DOUBLER are applied to the PCB-RGB. Figure 5-10 shows the PCBRGB circuitry. All three signals, Y, Cb and Cr, are processed by Enhancement circuitry in IC2D00. The enhancement is mainly aperture improvement, sharpening vertical lines in the picture. All three output signals are then applied to IC2B00. IC2B00 is called the Multi Component Processor. In addition to some signal switching, it is basically the RGB signal section of a VCJ. The Y, Cb and Cr signals are matrixed to form Red, Green and Blue Video Signals. The RGB signals are then processed by conventional RGB Drive and Cutoff circuitry, and are output at pin 35, 37 and 39 of the IC, respectively. AKB (Auto Kine Bias) circuitry is also used, adding an AKB pulse during the Vertical Blanking Interval of each signal. During vertical blanking, the AKB pulses drive the CRTs to conduction. At the


point of conduction, a Current Detector outputs the AKB pulse, which is fed back to pin 41 IC2B00. The internal circuitry automatically adjusts the CRT Cutoff bias if the CRT's characteristics have changed. DVD Component or DTV Inputs IC2B00 also serves as the input circuit for signal from the DTV and DVD Video Jacks. If necessary, the RGB signals from the DTV Inputs are converted to Y, Cb and Cr by an internal Matrix. The component signals are then output at pins 76, 77 and 78. The signals then take two paths: 1) To the SD/DVD Select Circuitry on the PCB-SIGNAL 2) Back to IC2B00 at pins 73, 74 and 75. When signal is present at the DTV or DVD Video Inputs, it is either in the 480i, 480p or 1080i format. The 480i horizontal frequency is 15.75 KHZ, 480p is 31.5 KHZ and the 1080i frequency is 33.75 KHZ. Horizontal and Vertical Sync from either the HDI (High Definition Interface) Inputs, Y inputs, or Sync on Green RGB input is applied to

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IC2B00. Sync is then routed to the uPC, IC700 where an internal Sync Detection Circuit automatically detects the horizontal frequency. The uPC then uses I2C control to route the signals accordingly. If the signals are 1080i or 480p, an internal switch selects the Y, Cb and Cr signals at pins 73, 74 and 75 of IC2B00 as the source to be converted back to RGB for the outputs at pins 35, 37 and 39. When the signals are 480i, the internal switch selects the Y, Cb and Cr signals at pins 67, 68 and 69. If the SD/DVD signal has been selected by the switch circuitry on the PCB-SIGNAL, these signals are the SD/DVD signals with line doubling. The RGB signals output from pins 35, 37 and 39 are then directed to the CRT's Color Output circuitry on the PCB-CRTs.

On Screen Display IC2B00 is also used to insert On-Screen Displays. On-Screen Displays (OSDs) include: User displays channel numbers, etc. User menus for initial setup, accessing advanced features, etc. Closed Captions Service and Convergence Mode displays The OSD signals for user displays, closed caption and the Service Adjustment Mode are generated in IC701, the Sub Microprocessor. The Convergence Mode crosshatch display is generated in IC800, the Convergence Waveform Generator. Figure 5-11 illustrates a Simplified Diagram of the V16 OSD circuitry. User, closed captions, and adjustment OSD signals are applied to pins 50, 51 and 52. The convergence crosshatch display signals are input at pins 46, 47 and 48 of the IC. The CONV-BK signal from IC800 is applied to pin 45 of IC2B00 as the timing signal for convergence crosshatch OSD insertion. The YS signal from pin 41 of IC701 is the insert timing signal for the OSD signals input at pins 50, 51 and 52 of IC2B00. The YS signal is buffered by IC710 and applied to pin 49 of IC2B00. Note that the YS and YM signals from the Sub Microprocessor are combined and both are applied to pin 49 of IC2B00. The YM signal activates the transparent background for the Closed Caption display. In the background area the YM signal reduces the main picture signals amplitude by one half. This produces the effect of a transparent gray background. The YS signal times the insertion of the OSD.

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