Assembly color TV secondary boot difficult maintenance case sharing - appliance repair - Huaqiang electronic network

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Shunuo varistor / ESD varistor / product complete / Sunlord first-class agent

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Photocoupler

Today, the store sampled home, and the home received a 21-brand TV, the user left the machine difficult to boot twice.
When picking up the screwdriver and opening the cover, I found that the back cover screw is not tightened. Is it a rework machine? The condensate was a little late, I wanted to abandon it, I was afraid that it would be expanded after the repair and repair, but the user did not leave the phone, and now it is not very busy, or turned on the TV.
When you open the board, you can see that it is a mess, a super chip, a memory, and the pulse related to the boot, the push, the standby control, the crystal oscillator, etc. are passive, and several components are not restored on the back.
Measure B+ voltage 110V, measure memory 8 feet only 2V, since it only has 2V, it must first check the cause, and the line is always found to switch the transformer 12V output A point, both are 2V, the load is not short-circuited, the welding limit flow resistance R558 A point is still 2V, the other voltages are normal, the load has been disconnected, this voltage will be only 2V? The diode is normal and there is a charging phenomenon. Even if the filter fails, it will not be so low. However, the filtering failure rate is quite high, or try to connect the 470UF capacitor first. The voltage at the A point is 12V, and the R558 is soldered. The TV is normal. Remove the C554 and measure its capacity to about 40UF. The capacitor's failure voltage should be 7 or 8V. The reason is low. The voltage is low, the CPU can't work, the load is light, and the power frequency is reduced. When the fault capacitance of this machine is not changed, B+ is connected to 60W bulb. When the load is aggravated, the voltage at point A rises from 2V to 10V. This is a very common fault but was repaired by the former repairer. Related to the second boot, should not be a novice, this post may be helpful to novices.

Supplement: This machine user has mastered the law. In the morning, the user takes the TV. He said that the TV can be turned on quickly by pressing the switch for more than ten times. The reason is analyzed: when the power is turned off, when the 300V main power supply is falling, the power supply oscillation frequency is correspondingly increased. High, the potential at point A will also rise, so that the continuous switch makes the voltage at point A reach the CPU working potential. As long as the line works, the load is aggravated, and the power frequency is increased, this TV is basically normal.