This document is a service manual for a COLOR TELEVISION model LET3250 (TS3250). It provides comprehensive information for professional service personnel, covering safety, alignment, debugging, block diagrams, and a detailed parts list.
Function Description
The LET3250 (TS3250) is a color television receiver. Its core functions include receiving and processing RF and AV signals to display color images and output audio. The television incorporates a main IC (LA76930/932) that handles various signal processing tasks, including video, chroma, deflection, and sound. It supports multiple input sources, including RF (tuner), AV (composite video and audio), and S-Video. The television also features an On-Screen Display (OSD) for user interface and control.
Important Technical Specifications
Main IC: LA76930/932 (CPU+1CHIP PAL/NTSC)
Tuner: T101
Audio Amplifier: AN7522
Power Supply IC: FSCQ1265RT
Deflection IC: LA78041
Memory IC: M24C08 (EEPROM)
High Voltage:
- Normal value: below 31.5kV at 1.6A beam current.
- Maximum limit: must not exceed 33kV.
Video Input/Output:
- VIDEO IN: 1 Vp-p 75OHM
- S interface Y IN: 1 Vp-p 75OHM
- DVD Y IN: 1 Vp-p 75OHM
- C IN: 0.3 Vp-p 75OHM
- Cr IN: 0.7 Vp-p 75OHM
- Cb IN: 0.7 Vp-p 75OHM
Audio Input/Output:
- AUDIO IN: <8x3>ohm>47 KOHM
Power Supply:
- AC power line: 120V/110V (indicated on the block diagram).
- Internal voltages: 5V, 8V, 9V, 14V, 28V, 110V, and high voltage (EHV).
Signal Processing:
- IF frequency: 45.75MHZ (VIF SW setting).
- Sound IF: 4.5MHZ (SIF SW setting).
- Color system: PAL/NTSC (indicated by the main IC).
- Horizontal and vertical deflection control.
- Automatic Gain Control (AGC) for RF signals.
- White balance and sub-brightness adjustment.
- Color trap filter and color band filter.
- X-ray protection.
EEPROM Settings (Factory Menu Adjustment Model Pre-set):
- P1-60 (60Hz Field):
- V SIZE: 63 (amplitude)
- V SHIFT: 0 (center)
- H-PHASE: 15 (H-center)
- V LINE: 15 (V-line)
- V SC: 23 (field S-correct)
- V COMP: 7 (field amplitude compensate)
- L.BLK: 7 (Left blanking)
- R.BLK: 0 (Right blanking)
- P2-EW-60 (60Hz EW):
- COR.SW: 1 (margin correct)
- H.SIZE.COMP: 7 (High voltage compensate)
- TILT: 44 (echelon correct)
- DC: 32 (H-amplitude)
- AMP: 25 (pincushion correct)
- COR.TOP: 4 (Top margin correct)
- COR.BOT: 3 (bottom margin correct)
- P3-50 (50Hz Field):
- V SIZE: 75 (amplitude)
- V SHIFT: 0 (center)
- H-PHASE: 10 (H-center)
- V LINE: 16 (V-line)
- V SC: 20 (field S-correct)
- P4 EW-50 (50Hz EW):
- TITL: 49 (echelon correct)
- DC: 35 (H-amplitude)
- AMP: 41 (pincushion correct)
- COR.TOP: 6 (Top margin correct)
- COR.BOT: 10 (bottom margin correct)
- P5 (Picture Settings):
- LINE: 0 (Level bright line)
- RB, GB, BB: 100 (Red, Green, Blue cut off)
- RD, GD, BD: 100, 15, 100 (Red, Green, Blue driver)
- P6 (AGC/Brightness/Contrast):
- RF AGC: 30
- SUB-BRI: 60 (Sub-brightness)
- SUB-CNT: 31 (Sub-contrast)
- P7 (Color/OSD/Sound):
- SUB-COL: 3 (Sub-colour)
- SUB-SHP: 0 (Sub-definition)
- SUB-TINT: 28 (Sub-tint)
- VOL.FIL: 0 (Volume control ADC filter)
- OSD.COT: 5 (OSD contrast)
- OSD.HPOS: 10 (OSD center)
- AFT: 0 (Line AFC loop gain and sync gate switch)
- VIF SW: 3 (IF3=45.75MHZ)
- SIF SW: 0 (Sound IF0=4.5MHZ)
- VIDEO LEVEL: 2
- P8 (Demodulation/Color Trap):
- A2.SW: 0
- GY ANGLE: 0 (G-Y demodulation angle)
- V.R TM: 0 (Filed scan starting time)
- R/B ANG: 8 (R-Y/B-Y demodulation angle)
- R/B BAL: 8 (R-Y/B-Y demodulation balance)
- C TRAP: 6 (Color trap filter)
- H FREQ: 16 (H-frequency)
- C.BPF TEST: 0 (Color band filter center frequency)
- P9 (Over-modulation/Dark Level/Color VCO):
- OVER.MOD.SW: 0 (Selection over-modulation function)
- OVER.MOD.LVL: 0 (Adjustment over-modulation working point)
- BLK.STR: 2 (Dark level expand starting control point)
- BLK.GAIN: 2 (Dark level expand gain)
- Y.APF: 1 (Selection color trap filter)
- PRE.ADJ: 3 (Pre-shoot)
- OVER ADJ: 3 (overshoot)
- C.VCO.ADJ: 4 (Color VCO frequency adjustment)
- P10 (Brightness ABL/White Peak/Field Blanking):
- BRT.ABL.DEF: 0 (Brightness ABL)
- MID.STP.DEF: 0 (ABL start control point)
- BRT.ABL.THR: 7 (ABL threshold)
- WPL.OPE: 2 (White peak limit)
- V BLK.SW: 0 (Field blanking switch)
- P11 (FBP/Noise Reduction/RGB Temp):
- FBP BLK SW: 1 (Horizontal blanking switch)
- DC REST: 1 (DC recover rate)
- CD.MODE: 0 (Field frequency division model)
- CORE GAIN: 2 (Noise reduction)
- r.GAMA: 0 (r-correct)
- RGB TEMP.SW: 1 (RGB DC output temperature speciality)
- A.MONI SW: 1 (Selection pin5 output)
- SVO OR FSC: 0 (Selection pin5 output)
- CROSS B/W: 0 (Selection test signal)
- CRAY.MODE: 0 (Test signal)
- P12 (Chromatism/Sound Trap/Brightness/Contrast):
- BY TV: 8 (Blue chromatism DC level)
- RY TV: 8 (Red chromatism DC level)
- BY YUV: 8 (DVD input Blue chromatism DC level)
- RY YUV: 8 (DVD input Red chromatism DC level)
- S.TRAP.TEST: 6 (Sound trap filter adjustment)
- LOW.BRI: 28 (Min-brightness)
- LOW.CONT: 30 (Min-contrast)
- P13 (Achromatic/VCO/VM Gain):
- COL.KILL: 7 (Achromatic level)
- VCO.FREQ: 32 (VCO frequency)
- VM.GAIM: 0 (VM gain adjustment)
- VM.DELAY ADJ: 0 (VM relay time adjustment)
- VCO TEST: 0 (VCO adjustment)
- VPOS-50: 15 (50HZ field center voltage adjustment)
- VPOS-60: 15 (60HZ field center voltage adjustment)
- P14 (Y/C Gain/Offset):
- Y GAIN: 0
- Y TH: 0
- B OFFSET: 0
- B WIDTH: 0
- C OFFSET: 0
- C WIDTH: 0
- CAN.V CHIP: 0/1 (V-CHIP)
- OPTION (AV/MTS/Power/Volume):
- AV: 3 (AV selection: AV1/AV2/S/DVD)
- MTS: 1/0 (MTS IC selection: 72700/AN5832)
- V.OFF.MOTE: 1 (Turn off model)
- PWR.MEM: 0/2 (Turn on model: standby/auto turn on/memory)
- 1115: 0 (select LV1115)
- BLCK GROND: 1 (No signal background selection: blue/black background)
- N/PN: 1/0 (South America and North America selection)
- PWM.VOL: 1 (Volume control of PWM set)
- 1-CHIP.VOL: 0 (Volume control of mono)
- VOL 1, 25, 50, 75: 20, 60, 90, 100 (Volume control speciality)
- ALC: 1 (ALC)
- VOL: 0 (Baseband model, input level adjustment)
- SAP LEVEL: 1 (SAP level)
- SIF.M/BB.M: 0 (SIF and baseband model)
- AGC: 1
Usage Features
The television is designed for standard home entertainment use, offering multiple input options for connecting various external devices like DVD players, gaming consoles, or other video sources. The OSD allows users to adjust picture and sound settings, as well as other operational parameters. Remote control functionality is supported for convenient operation.
Maintenance Features
Safety Precautions:
- X-RAY RADIATION PRECAUTION: Emphasizes the importance of maintaining high voltage within specified limits (below 31.5kV, not exceeding 33kV) to prevent X-ray radiation hazards. The picture tube is identified as the primary source of X-ray radiation, requiring replacement with the exact specified type.
- General Safety: Advises the use of an isolation transformer during dynamic service, discharging the picture tube anode before handling, and ensuring all protective devices (knobs, covers, shields) are reinstalled after servicing.
- Part Replacement: Stresses the use of specified replacement parts, especially for safety-related components (shaded in the schematic and parts list), to avoid risks of shock, fire, or X-ray radiation.
- Fuse Replacement: Specifies replacing blown fuses only with the FUSE type listed in the chassis parts list.
- Component Spacing: Recommends keeping high wattage resistors at least 10mm (1/2in) away from the circuit board.
- Wiring: Connection wires must be kept away from high voltage or high-temperature components.
Alignment and Debugging Procedures:
The manual outlines a detailed alignment flow chart and debugging instructions for various parameters:
- EEPROM Copy: Initial step for setting up the television's memory.
- B+ Check: Verifying the B+ voltage (negative pole of VD509) to be 135V±2.
- AGC Adjustment: Measuring RF AGC voltage (V1=4V±0.2V, V2=3.5V±0.2V) and adjusting the picture for proper signal reception.
- White Balance and Screen-Grid Voltage Adjustment: Adjusting white balance using a remote sensor and setting the screen-grid potentiometer on the FBT for horizontal bright line.
- Color Purity and Assembly: Adjusting color purity and convergence.
- High Voltage and Filament Voltage Check: Measuring high voltage (29kV±1.5kV) and filament voltage (6.3±0.1Vrms).
- X-ray Protection Check: Verifying X-ray protection by turning off the power source and measuring the return to normal within 30 seconds.
- AV Function Check: Verifying AV input impedance and signal levels.
- AV Parts Check: Inspecting and verifying AV and crossfire, allophone, remote control, and color purity.
- Leave Factory State Setup: Finalizing settings before leaving the factory state.
- Check: General verification of the television's functionality.
- Safety Check: Final safety inspection.
Test Equipment:
- AUDIO VOLTAMETER
- OSCILLOGRAPH
- HIGH-VOLTAMETER
- DIGITAL MULTIMETER
- AC ATTACK PULL TEST EQUIPMENT
- SCAN frequency signal generator BT-3
Exploded View and Part List:
The manual includes an exploded view diagram of the television components and a comprehensive part list, detailing each component's description and part number. This is crucial for identifying and ordering replacement parts during repair.
Wiring Diagram:
A wiring diagram illustrates the interconnections between different boards (CRT board, Key board, AV board, Mainboard) and components (Tuner, FBT, Speaker, Power supply, Main IC, Memory, IR RX/TX, Audio Amp). This helps in troubleshooting connectivity issues.
Block Diagram:
The block diagrams for the main system and the main IC (LA76930) provide a high-level overview of the signal flow and functional blocks within the television, aiding in understanding the device's architecture and pinpointing problem areas.
Pin Function Introduction:
A detailed table lists the function and reference voltage for each pin of the main IC, which is essential for diagnosing issues at the IC level.
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