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Samsung 46-inch LCD screen, high-voltage board repair diagram

In Electronic Infomation Category: S | on November 18,2011

0.0/0.1 version of the Samsung 46 inches LCD backlight system consists of about two backlight driver board, a motherboard (Master) A board or call the other one is from the board (Slave) or call B boards, work A, B cable to connect two panels to achieve synchronization. A backlight control circuit MSC1691AI panels to the core, together with the excitation light output and MM74HC4316M datasheet and current distribution circuit, B boards only light excitation, output and MM74HC4316M price and current distribution circuit. Each plate has two step-up transformers, each with step-up transformer current distribution transformers 12 and MM74HC4316M suppliers and 6 output sockets, drive 12 CCFL lamp, its block diagram shown in Figure 1.

block diagram in Figure 1

each step-up transformers and their corresponding excitation IC (OZ9981GN), 4 two MOSFET tube to form a light-driven channel, so that A and B panels backlight driver board a total of four channels.

A, B input socket CNl01/CN401 board of ~ and ~ feet feet provide 24V power to the backlight circuit, but the backlight brightness level and adjusts the PWM control signal input to only A panel input jack CNl01 of (12) feet and (13) feet.

Samsung 46 inches REV: OO and REV: 0.1 two versions of the same circuit structure, the only difference is the shape of the output socket, shown in Figure 2. Under two light boards around both ends of the cable connections for cascading outlet, the actual use of two cascaded cable connections shown in Figure 3,4.

Figure 2

Figure 3

Figure 4

one major IC Introduction

1.MSC1691 (IC101) Backlight control IC

MSC1691 is MicrosEMIs a low-cost, enhanced, can directly drive the CCFL controller, the internal converter for palm-based PDA (personal digital processor, often called palm only computer) to large-screen LCD TV CCFL backlight control. Built-in digital and analog PWM brightness control and over-voltage over-current protection circuit.

MSC1691 16-pin TSSOP package, the internal block diagram shown in Figure 5, the typical application circuit shown in Figure 6, the measured voltage and the pin functions in Table 1. < / P>

Figure 5 Internal Block Diagram

Figure 6 Typical Application Circuit

following key pin on the MSC1691 circuit analysis.

(1) (16) feet, VDDP Duanyou 24V power supply output by the voltage regulator circuit stable 5V-VCC voltage supply to the foot VDDP power, other power supply circuit shown in Figure 7.

power supply situation in Figure 7

(2) , feet, AOUT / BOUT excitation pulse output signal, shown in Figure 8.

Figure 8

(3) feet, ENA (Enable) side of the foot lamps enable the IC to run or not to enable, or a lamp lit the control side, as shown in Figure 9 as shown. If the pin is high, all functions are enabled, IC starts running, the lamp is lit; if low, internal power supply and disconnect VDDP pins, disable all of the features, IC stops working, the lamp goes out.

Figure 9

(4) feet, VDDA (Reference) to form the reference voltage terminal

the foot by foot by the internal power supply terminal VCC regulator output after a 3V reference voltage for the IC and the external circuit, when the IC protection, the feet are not output.

(5) (13) feet, OV-SNS over-voltage sensing input voltage through the voltage sensor detection signal sampling circuit, got a lamp for voltage proportional to the midpoint and full-wave AC voltage OV-SNS. and then by full-wave rectifier, and then added to the IC internal reference voltage of 2V on the comparison. Pin input signal from the frequency range of 10kHz ~ 500kHz. Normal operation, the pin voltage is +2 V range, when the sensor input signal voltage exceeds + /-2V, the internal digital comparator rollover occurs, the protection from the control circuit, IC is disabled, the lamp goes out. In practice, this pin is not used.

(6) feet, OC-SNS over-current detection input) side current sensing detection signal through the current sampling circuit, the input for the mid-point with a high-voltage transformer secondary current is proportional to the The full-wave AC voltage OC-SNS, and then added to the ICs internal reference voltage of 2V for the digital comparator is shown in Figure 10. Such as. If sustained peak voltage greater than 2V, the internal digital comparator rollover occurs, the protection circuit from the control.

Figure 10

2.029981GN (IC * 02) dual channel actuator

Each channel has an actuator backlight, so A, B board has four 029981GN, the light excitation and the oscillation signal sent by the composition of the bridge MOSFET and transformer power output circuit .

3.BA2901F (IC103/204/303)

BA2901F Rohm Corporation is a quad voltage comparator, using SOP14 package, the internal circuit diagram shown in Figure 11.

internal circuit diagram of Figure 11

Second, the unit circuit diagram

high-voltage transformer and current distribution circuit shown in Figure 12, PWM control circuit shown in Figure 13, the power excitation circuit shown in Figure 14, over-voltage protection circuit shown in Figure 15, overload protection circuit shown in Figure 16, 17.

Figure 12 high-voltage transformer and current distribution circuit

Figure 13 PWM control circuit

power excitation circuit diagram 14

Fig 15 overvoltage protection circuit

overload protection circuit Figure 16

overload protection circuit Figure 17

Third, the technological transformation program

symptoms: early adopters Samsung 46-inch LCD screen TV, the backlight it with the 0.0 version of these machines in use for some time, will appear from time to time the backlight off failure to be re-boot the machine after cooling, the backlight can light up.

failure reasons: in the sample over-voltage protection circuit board, the distribution of capacitance with voltage fear C180, C280, C380, C480 performance is poor (Figure 15), its capacity with temperature The change, which led to false start protection circuit.


1. The C180, C280, C380, C480 changed to a smaller capacity affected by temperature ceramic chip capacitors, capacity of 2200pF.

2. The MSC1691 (14) feet of the anti-interference capacitor C120 to external ceramic chip capacitors, increasing capacity from 220pF to 2200pF.

[Note] real repair of such failure, if short pad UP A panel (Figure 18), will cause high pressure drop, reducing the lamp intensity, this method desirable; if MSC1691 (14) feet or on the C120 and then a 4.7F capacitor, it would greatly reduce the sensitivity of over-voltage protection is still not desirable; if the short circuit R182 or R139, R172 to increase the resistance, or cancel the resistance R137, will reduce the protection threshold, or even cancel the over-voltage, overload protection, so that is not acceptable.

Figure 18

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