Philips 93R movement color TV line / field / protection circuit principle - Power Circuit - Circuit Diagram - Huaqiang Electronic Network

LC03-3.3 SOP8 TVS Static Protection 3.3V

In the color TV of the 93R movement, the small signal processing circuit adopts TDA8841 (bit number 7250, the same below), the field output circuit adopts TDA9302H (7460), and the microprocessor (CPU) adopts SAA5542PS (7600) (different models, The CPU integrated chip suffix used may be slightly different), the memory uses 24C08 (7601), the sound amplifier circuit adopts TDA7056 (7953), and the switching power supply oscillation/pulse width adjustment/protection circuit adopts MC44603P. In the past few years, the TDA884X/OM883X series chips have been used as the core processing circuit, and a large number of TV sets have been produced. Philips TV's TV opportunities have produced many strange and unexpected failures, especially the TV sets of the TDA884X/OM883X series, which are different from the different designs, different models and different control software of different manufacturers. The phenomenon may also be different, these are well known to the vast majority of maintenance peers.

Philips 93R movement, in the design of the circuit is very distinctive, there are a variety of protection circuits, maintenance information is difficult, the manufacturer has not paid the relevant circuit schematics, so the maintenance work is difficult.

Taking Philips 21PT3520/93R color TV as an example, the line, field, protection circuit and CPU control circuit of the machine are drawn according to the physical object, and the working principle is briefly analyzed. Finally, two maintenance examples are introduced to help the work of the peers. .

The relevant circuit is shown in Figure 1.

1, the line start circuit.

The machine is equipped with a line start circuit with the time base circuit NE555 (7607) as the core, and no similar design is found in the domestic machine. In this machine, the NE555 and its peripheral components 3610, 3611, and 2608 form a multivibrator with an oscillation frequency of f=1.443/(3610+3611)2608, which mainly provides a start pulse signal for the row excitation stage and the line output stage. When the power of the machine is turned on, the switching power supply starts to work, and the three sets of voltages of +9V, +16V, and +95V are output from the secondary. Among them, +16V is the power supply for the sound amplifier circuit 7953; +95V is the line excitation stage and the line output stage; the +9V voltage is stabilized into +5V and +3.5V voltages through the triode 7612 (BDl35), 7602 (BD135) and other components (see Figure 3) on page 13, where +3.5V supplies power to the CPU (7600). In addition to supplying voltage to the 7600 interface circuit, +5V supplies power to the 8-pin of the row start circuit 7607. When the 76078 pin is powered by +5V, the internal circuit begins to oscillate. The start pulse is output from pin 3, first amplified by transistor 7608 (1F), then further amplified by row driver stage 7400 (BF422), and finally coupled by row excitation transformer 5444. To the b-pole of the output tube 7402, the row output circuit is driven to operate.

2. Line normal working circuit.

Under the excitation of the row start pulse, the row output tube 7402 operates in the switch state, and the line output transformer 5445 has an alternating current flowing through the primary 12 winding, and a line reverse pulse induced on the winding of the secondary 3 leg, via 6412, 2415. After rectification and filtering, the voltage of +9V is obtained, and it is powered by the input of the center, the field, and the small signal processing circuit TDA8841 (7250) 12 and 37. The internal oscillating circuit of the 7250 starts to work, and the oscillating signal is subjected to a series of processing by internal circuits (such as synchronous separation circuit, line frequency dividing circuit, row AFC-1, AFC-2, etc.), and the excitation pulse is output from 40 feet. The signal is coupled to the circuit of the 76076 pin via the capacitor 2610 (332). After the internal circuit is processed, the excitation pulse is output from the 3 pin. After being amplified by the 7608 and 7400, the output tube 7402 is pushed to drive the row deflection coil to control the electron beam. Scanning in the horizontal direction, the whole circuit circuit begins to work formally.

3, line output transformer

5445 groups of the role of the reverse pulse and its direction. In addition to providing the required high voltage and medium voltage to the picture tube, the line output transformer 5445 is rectified by the 6412 and 2415 rectified and filtered to obtain a voltage of +9V for 7250; the 4-leg reverse pulse is rectified by 6410 and 2414. After the filtering, the +8V voltage is regulated by 7010 (7805) to +5V and then supplied to the high-frequency head and other circuits. The 56-step line reversal pulse is obtained by the 6402/24lO, 6405/2417 rectification and filtering circuit to obtain the voltage of ±14V. , the field output circuit 7460 (TDA9302H) power supply; 7-pin line reverse pulse through the 6413, 2413 rectifier filter circuit to get +195V voltage, for the visual amplifier circuit power supply; 8 feet for the high-voltage ABL terminal; 9-pin line reverse pulse In addition to powering the picture tube filament, it also provides a detection signal for the protection circuit.

In addition, the row return pulse of the row output tube 7402c passes through the 2406/2405, 3404 resistance volume fraction, and the 6420 and 6421 clamps are divided into two paths: one of which is sent to the 7250 line back pulse input via 2237, 2238/3268/ Fortress pulse output terminal 41 (acts as follows); the other channel is divided by 3633, 3634, after 7610 amplification, is sent to the 36 feet of the CPU (7600) to determine the horizontal position of the character display.

4. "Open, wait" machine control circuit.

After the 9th and 37th pins of the 7250 are powered by +9V, the internal line oscillating circuit starts to work, and the excitation pulse from the 40-pin output line is output to the 6th pin of the 7607, and the line start circuit 7607 completes its line start mission. At this time, the 7607 is only equivalent to an on/off switch to turn on or off the line excitation pulse output of the 3 pin, that is, the "on/off" machine control function. In Figure 1, the "on/off" control terminal 19 of the CPU (7600) is connected to the 4 pin of the 7607, whether it is the row start pulse generated by the 7607 itself or the row excitation pulse from the 7250 40 pin to its 6 pin. Whether the pulse can be output from the 76073 pin is determined by the voltage of the 4 pin. In the power-on state, the CPU 19 pin is +5V high level due to the internal circuit cutoff, the 76074 pin voltage is high level, the internal circuit turns on the signal output of the 3 pin, and the line circuit obtains the excitation signal and enters the normal working state: On the contrary, the internal circuit of the CPU 19 pin is turned on and is low level, the 76074 pin is low level, the internal circuit cuts off the line excitation pulse output of the 3 pin, the line circuit loses the excitation pulse and stops working, and the whole machine is in the standby state. The measured operating voltage of NE555 is as shown in Table 1.

Foot number/item

1

2

3

4

5

6

7

8

Features

Ground

Line start oscillation

Line frequency output

On, standby

air

Row oscillation

Row oscillation

powered by

Power on state

0

2.44

2.35

5.45

3.67

2.45

2.94

5.51

standby mode

0

0.11

0

0

3.6

0.1

0.1

5.12

Fault status

0

2.85

2.29

4.18

3.72

2.85

2.85

5.59