1 introduction
When television technology teaching, the electric circuit is complex, each kind of part has the breakdown phenomenon regarding the television to demonstrate with difficulty on the screen, the teacher can only depend upon the principle analysis to make the judgment, is separated from the circuitry and the material object, causes the student difficultly to study, the teacher difficult to teach common phenomenon. But when student actual operation, the signal flow is not direct-viewing, has the suitable risk. In view of these questions, has given one kind based on the I2C main line’s remote control color television principle and the breakdown demonstration installment, enlarges the form the television internal circuit’s part and circuit schematic diagram to demonstrate, strengthened the teaching scene feeling and the third dimension.
2 overall project design
2.1 television cassette mechanism choice
Television’s type divides according to the integration rate has the scale, large-scale and the ultra large scale integrated circuit remote control color TV set; Has the small screen, the medium screen, the large screen color TV set according to the screen size minute; Has the right angle plane, the planoid, the entire plane, the mirror surface, the pure plane color TV set according to flatness aspect minute. Considered from the course content that mainly introduces the Toshiba two, four piece of machine large scale integrated circuit color TV set principle and the service technology and the ultra large-scale monolithic integrated circuit’s color TV set principle.
According to above factor consideration, therefore selects the Sanyo monolithic integrated circuit LA76818A,2l inch plane right angle teletron, take LC8635-28CP as the CPU external guidance system, has designed the 2l inch right angle plane remote control color TV set principle and the breakdown demonstration installment. Chart l is the Sanyo monolithic cassette mechanism complete machine circuit diagram.
The LA76818 cassette mechanism is Sanyo Corporation take one piece type integrated circuit LA76818 as the large-scale small signal processing electric circuit cassette mechanism primarily. The LA76818 interior including image/sound accompaniment intermediate frequency processing, brightness/chrominance signal processing, the line/deflects the small signal processing electric circuit and so on, does not need the external connection lH baseband delay line. When processes the SECAM system signal, so long as external connection exempts debugs SECAM demodulation electric circuit LA7642 then. The cassette mechanism function is realizes by Sanyo Corporation microprocessor LC863348A after the I2C main line.
2.2 complete machine structural design
The circuit wafer size must choose big as far as possible, satisfies when the explanation color television principle and the breakdown demonstration long-distance range onlooking request. Grows 2.4 meters with two duplicate copper plate splicing, the width 1.2 meters circuit wafers. Frontage draws the circuitry schematic diagram, and installs the part nearby the mark, manufactures the printing circuit diagram in the back, connects the part. After television’s type and circuit wafer size designation, carries on the layout to various part of electric circuits. The frame uses rectangular and the square shape empty stomach steel products composition, the board right bottom leaves leeway installs teletron’s position, fixes with the rivet two duplicate copper plates on the frame, between two duplicate copper plate’s perfect fittings of seams use the galvanized iron sheet soldering connection. The foundation design needs to guarantee that the entire equipment is balanced, the foot is loaded with 4 oak rubber tires.
3 electric circuit schematic diagrams
Electric circuit schematic diagram accurate direct decision complete machine performance. To prints in the circuit diagram according to the schematic diagram the part to carry on the layout, is a complete color television schematic diagram directly, installs the part nearby the part mark, is advantageous for in the teaching to test, the explanation principle as well as the breakdown demonstration. This equipment electric circuit schematic diagram and the printing circuit diagram’s design is completely different with the common electronic installation. Regarding the teaching installment, is convenient for the teaching, the schematic diagram and the printed circuit should design big somewhat, is advantageous for the student long-distance range onlooking.
Will design 2.4 m×1.2 m the printed wiring boards to have each kind of disturbance. Therefore, when designa circuit schematic diagram must consider the signal the integrity and electric circuit’s antijamming technology. When electric circuit schematic diagram design, the signal flow from top to bottom or from left to right, the use walks the line should alternately to be as far as possible few, the holding wire should as far as possible short reduce the distributed capacity which, the leakage inductance, because the line is excessively long causes.
Because design’s circuit diagram can only use the printer printout using Protel99 the SE, is incompatible with other softwares, the document format cannot replace. If SCH under document copying Photoshop, after the enlargement, the image changes empty. Therefore needs to use the Photoshop software plan circuit diagram.
4 printing circuit diagrams
According to the electric current size, widens the wiring as far as possible. The power line, the grounding trend should be consistent with the signal direction. In the board power source input end receives on 10~100 μF decoupling electric capacities. The digit separates with the simulation. Meets the grounding to overstrike as far as possible, can through 3 times on the printed wiring board permissible current, the wiring line width be supposed at least to reach 5~8 mm generally. Meets the grounding to constitute the endless loop return route as far as possible, like this reduces the grounding potential difference.
4.1 printed wiring board antijamming design
When television’s complete machine system design, should consider and satisfy the anti-jamming fully request, avoids after the design completes increases the antijamming again the remedial treatment. Antijamming design basic principle: Suppresses the noise source, enhances sensitive unit’s anti-jamming. Because the high frequency interference noise and wanted signal’s frequency band is different, therefore may filter the high frequency interference through the filter, may also use isolates the light pair solution. Wants the special attention to suppress. But suppresses the radiated interference through to increase the noise source and sensitive unit’s distance it, the right-of-way line isolates or installs on the sensitive unit the screening can.
4.2 printed wiring board chart design
Needs the thorough understanding to select the part and each kind of plug’s specification, the size area and so on. From aspects and so on electromagnetic field compatibility, antijamming ability considered that determines part’s layout.
on 4.3 duplicate copper plates prints the circuit diagram
The printing circuit diagram is take the schematic diagram as a datum, uses the Protel99SE plan. Each part has the relevant position, prints in the circuit diagram in part’s installment position and the schematic diagram part position corresponds. Photoshop outputs when the PCB chart certainly wants the mirror image, will then print the circuit diagram to photocopy with the carbon paper on the duplicate copper plate, the attention line is even. After the photocopying, unmistakable may drill a hole after the overall check installs the part.
When drill hole first wants the precision measuring related special part’s pin to be away from, the aperture size, specially the integrated circuit, the transformer, the time delay line and so on essential part, then the definite hole position, drills with the electric hand-drill.
On the duplicate copper plate should draw the good printing chart to spread completely the full paint, forms the big area earth, the attention line edge must be smooth, the curving part should spread the full circle angle, around the part hole must maintain certain distance, is advantageous for the part welding.
4.4 printed wiring board corrosion
What the corrosion printed circuit usually uses is the iron trichloride peroxide solution, here uses the hydrogen peroxide solution to add the hydrochloric acid the peroxide solution to carry on the corrosion, will turn round on the copper plate not to paint the part the copper sheet to play the part of spoiled. On printed wiring board’s paint will wash off with the gasoline, when wash the circuit wafer must lay aside vertical, prevents excessively many gasolines to flow to the positive influence schematic diagram through the hole.
4.5 part examinations
According to the Sanyo LA76818A monolithic integrated circuit complete machine circuit diagram, uses Protel99 the SE automatic production part tabulation, compiles this equipment to use in common 341 parts. According to part category induction part name, quantity, model and parameter. Must examine its main performance index and the characteristic request regarding the essential part.
5 circuitry’s installment and debugging
Before installing, must to each kind of part’s wire, the switch, the potentiometer, the connector carry on the prior operation, including: Welding position’s dipping soldering, part pin dipping soldering and the forming, the wire and the jumper wire yummy treats, skin, dipping soldering.
5.1 breakdown demonstration part
Before installing the complete machine part, must determine that the breakdown demonstration must replace the part, definite principle: The common breakdown, easy to produce breakdown part. Should establish various spots many kinds of breakdowns. When establishment breakdown part must use peg grafting to carry on the installment. May act according to the different part pin the diameter to select the different aperture peg grafting.
5.2 complete machine printed wiring board installment
This breakdown demonstrates equipment’s all parts to install on 2.4 m×1.2 m line boards. Installs the resistance, the electric capacity, the diode, the triode, the inductance, the integrated circuit in turn first, then installment demonstration breakdown part’s peg grafting. When debugging installs the part, finally installs the joint wire and the jumper wire, should pay attention to various parts’ power source supply line to separate, prevents the printing plate short circuit and the welding bad creates the short circuit, interferes with the complete machine work, surveys and debugs when various part should the key examination.
6 television various circuit testing and debugging
6.1 power source adjustments
The digital voltmeter meets in the voltage out-port; Adjusts the potentiometer, causes its output the DC voltage is 115 V±0.2 V. So long as 115 V voltages are normal, the other 5 V, 12 V, 17 V, 24 V, 180 V voltages are also normal, otherwise, the power circuit has the question, should remove.
6.2 integrated circuits, transistor’s test
In the test circuit integrated circuit LA76818A, LC863528CP, TDA2003, an5522 various pins voltage should meet the system requirement. Specially when the CPU work, the supply voltage, the resetting voltage, the clock oscillating circuit should guarantee that the work is normal. Carries on the test parameter in triode’s static operating point.
in 6.3 puts the adjustment
In the sweep tester test puts electric circuit’s amplitude frequency characteristic, 38 MHz intermediate frequency television signal level is 60 dB, to 38.5 MHz, 30 MHz, 31.5 MHz intermediate frequency signals should have the varying degree absorption.
6.4 AGC adjustments
The day terminal input level is 60 dB PAL system radio-frequency signals, is in the I2C main line pattern. Adjusts the RFAGC data to cause monolithic integrated circuit LA76818A 4 pins to output puts the AGC voltage is high 2.4 V±O.05 V.
6.5 focusing electrodes, shield grid and white trimming
Before the debugging, complete machine preheating 5 minutes; Inputs the black and white test card, the signal strength is 70~80 dB, the adjustment focusing potentiometer, causes the image focusing to be best. Shield grid and white trimming according to explanation adjustment.
7 main line adjustments
7.1 service the main line
Adjusts the volume is smallest, “recalls” the key according to a remote control on, presses the volume “to reduce” again, according to “recalls” the key, enters the factory service pattern in turn. According to the channel fluctuation key “P ” or “P-” the key choice reconciliation item, selects the project the character to become red by the green. According to the volume fluctuation key “VOL ” or “VOL one” the key, the project data which the adjustment selected, after the adjustment had finished, closed down then withdraws from the factory service pattern.
7.2 main line adjustments
Enters the service main line adjustment pattern, the good center, the field pattern, field S adjust, the field center and the field height adjustment adjustment, according to the corresponding step adjustment, meets the requirements. With the avonmeter cocurrent files survey main line voltage, shows the needle instruction main line pulse voltage mean value, through the table needle instructed that the position is helpful to the judgment and the analysis electric circuit breakdown. Under this aircraft normal state’s main line voltage approximately is 4.3 V. If the main line voltage achieves 5 V supply voltages, simultaneously appears halts, should inspect reset circuit V802 whether to damage. Whether VD804 does short-circuit. If the main line voltage is 0 V, is at the readiness for action, possibly is the crystal oscillator X801 damage or the R835 opening. If the breakdown phenomenon is three does not have, the main line voltage swing, should inspect the N701 15th pin external connection the filter element whether to damage.
8 conclusions
Color television demonstration system installment application modern television new technology, in union present market commonly used color television typical circuit, expands through the design it the large-scale demonstrator. This may see intuitively the internal circuit, through the test point test circuit parameter, has facilitated the modern electronic information teaching and training enormously.
