As the protection of the machine is connected with the switch on / off circuit, the protection circuit is the main switch power supply, which is similar to the standby state. If the boot is a relay of sounds, and the responses, but can not boot, indicator from yellow to red, but you can not change to green, and then relay release, or boot without remote standby operation, the TV automatically shutdown, indicating lamp by the boot after the green to red or yellow... Can be judged to be the protection of the circuit work, into the protection of the state.

2 measure critical point voltage, judge the fault range

(1) to determine whether to enter the state of protection

Due to protection when take off the main switching power supply, if turning the moment has a + B voltage output, and then to 0V and can be determined is enter the state of protection; simultaneous measurement of ICl213 (6) pin voltage and standby control foot (33) voltage pin, if (6) voltage pin by a low level of normal variable is above high level 2.5V, also (33) voltage pin from the boot of the high level variable to a low level, can be judged is enter the state of protection.

(2) where the protection of the circuit is caused by the protection of the road

Boot into the protection of the moment, and measuring various protection execution circuit of trigger voltage and the microprocessor port voltage interruption, if D819 light-emitting diode anode (figure a), Q856 base (Figure b), Q858 base (Figure C) trigger voltage and microprocessor interrupt port for high level is separate element protection caused in the circuit protection; if protection execution circuit D819, Q856, Q858 (Figure A, B, c) no trigger voltage just microprocessor port interrupt for high level is caused by the fracture of circuit protection. If the Q856, Q858, D819 (Figure A, C, b), which is the way to protect the implementation of the circuit has a trigger voltage, you can determine the circuit protection circuit to start, causing the protection.

(3) judging by which way the fault detection circuit is protected

In determining the protection induced protection circuit to start, then forward measure to protect the executive circuit is connected to the fault detection circuit of the output voltage, focus on measuring the figure of D, e, F, G voltage, which detection circuit outputs a high level is the detection circuit and the detection circuit failure.

3 to lift the protection, observe the failure phenomenon

In order to ensure the maintenance of safety, to avoid the loss caused by the lifting of the protection, the proposed lifting of the protection, the first to take three measures:

One is removed, electric wave and double voltage rectifying automatic switching circuit IC895 and change for the full wave rectifier circuit to avoid because of the automatic switching circuit failure or malfunction caused by damage to the components of power; second, measuring the power and the line output circuit without obvious short circuit, open circuit fault, power thick film block and line output duct intact; the third is to disconnect the combined load, connected to the dummy load test machine, after B voltage is normal again, line output circuit for maintenance.

Due to the discrete element protection circuit is not through interrupts the microprocessor port detection and protection, so the discrete element protection circuit protection lift, not through the fracture in the implementation of release, disarm protection through the following methods:

(1) measures to take measures to remove the protective state from the standby circuit

Two methods: one is the standby control relay RL801 switch contact short-circuit directly the main power supply; second is at the base of the Q852 by LK resistor connected Deputy + 5V power supply, and broken open R854, make Q852 forced conduction, RL801 pull. After power on the power, observe the fault phenomenon, measure the voltage, according to the fault phenomenon and voltage to determine the scope of fault. At this point, the microprocessor is still in standby mode.

State, can not output the various control voltage, may have no light, silent failure, but can be the first test of the power supply and related circuits.

(2) measures to take measures to protect the implementation of the protection of the state

A short circuit and open circuit two methods: A is one by one short various protection execution circuit of trigger voltage, namely one by one light emitting diode negative short circuit D819, D553 D862 anode and the ground short circuit between the base and Q856 Q858; second is one by one to disconnect the various protection execution circuit and the standby control circuit connection, or directly removed protection element. Each short circuit or open circuit protection actuator, as a boot test, to observe the failure phenomenon, test, if the way in which the trigger voltage, or the removal of protection execution circuit and TV is no longer protected is protect the execution caused in the circuit protection, according to exit protection fault phenomenon, judge fault coverage, for further inspection.

(3) measures to take measures to remove the protective status from the failure detection circuit

In determining the way in which the execution caused in the circuit protection protection, also can restore the protection execution circuit, take one by one broken fault detection circuit which is connected with, the starting test, if the disconnection of the way in which the fault detection circuit and executive circuit connected, Boot Exit protection is the fault detection circuit and the detection circuit failure, caused by the protection.

(4) take measures to relieve the protection from the interruption

If the measures taken by the microprocessor did not enter the starting state, or has been confirmed is disruption of the induced by external fault detection circuit, the fracture measures to lift the protection, the method is: will fracture (6) feet of short circuit or interrupt port with an external disconnections.