TCL color TV AT34276 secondary boot does not start the maintenance process - android - Phones Developers

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More than ten o'clock last night, my friend called me to repair TV for his dad (know that I get up late during the day) The reason is that the elderly are retired cadres and the news in the morning must be seen.
Because the distance is not far (less than 1 km), the friendship is good, there is no reason to deny, so I have to come to the door.
There are two TVs: the old-fashioned 34" TCL and one 32" Skyworth LCD.
It is said that the 34" color TV can still watch normal during the day. When the TV is turned on at night, the indicator light is on, and the second startup cannot be started.
Model: TCL color TV AT34276
Overhaul process:
Press the power supply, the indicator light is on, check +B135V is normal, press the remote control switch to turn on the second time, +B will not start when it drops to 70V, then return to the standby state, +B rises to 135V again.
First check the line circuit: the line tube is normal, disconnect the high voltage package + B pin, use the universal meter 2.5A file to detect the line current. When the remote control switch key is pressed twice, the current will stop immediately after the current is less than 50ma, and then enter standby. status.
Suspected that +B load capacity is poor, check the filter capacitor, rectifier tube, are normal. Solder back to the high voltage package + B pin, the idea is to turn to the voltage regulator circuit.
The machine has three sets of power output: +135V supply line circuit, +16V supply sound amplifier circuit, +13V supply scan, CPU, voltage regulation sampling and other circuits. It seems that this voltage is doubtful.
Press the power switch, the voltage is measured at 11V in the standby state, press the remote control switch to start the TV, the voltage is immediately reduced to about 8V, obviously not normal!
Turn off the power supply, remove the filter capacitor C838 (2200UF/16V, the original machine drawings are wrong, marked as 1000UF/16V), because the capacitor is close to the current limiting resistor, the side has been baked and discolored, check the capacity, charge and discharge It is small and has obvious leakage. Because there is no capacitor of the same volume at hand, it is replaced with 1000UF/25V capacitor.
As for the maintenance of another TV set, by the way, the 32" Skyworth LCD does not turn on, the indicator light does not light, the teardown check, the power switch is not available, because Skyworth's accessories are different (four pins are diamond-shaped) There is no replacement of parts, emergency repairs are not connected to a group of wires, troubleshooting, repairing two TVs takes about 100 minutes.
TCL failure analysis: Since the circuit supplied by the 13V circuit is critical (as shown below), the TV cannot be started.

Seen from the red line in the figure, after 13V is divided by R830 and D826 is regulated to 5V, it is supplied to the storage and CPu circuit. After passing through the regulator IC, it is regulated to 8V to supply the scanning circuit. The most important thing is to pass R838 and R839. After partial voltage supply, the optocoupler and the sampling reference voltage regulator circuit are provided. Since the scan circuit has not been started in the standby state, the load is not large, so even if the filter bad voltage drops little, once the startup, the scan circuit works, the load increases, and the filter In the bad case, the 13V voltage drops immediately, which destroys the sampling and reference regulation conditions, causing the +B to drop and the scanning circuit not working properly. To this end, repair the fault with poor load capacity, when the +B circuit components, line circuit components are normal, you should consider the power supply circuit of the voltage regulator circuit!