T801 and T802 (4) - (6) Winding output pulse voltage, R802A, R804A, C801 Power supply output terminal load short-circuit, or rectifier filter circuit component breakdown led to the power supply output current is too large, the power output voltage. From the switching power supply regulator circuit and the standby control circuit analysis, we can draw the following conclusions: Standby control circuit is an auxiliary circuit in the switching power supply, the voltage regulator circuit is the main circuit switching power supply. Standby control circuit is designed to change the working state of the power supply, the control circuit of the standby control circuit is to control the result of the circuit is to promote the switching power supply in standby mode, the output voltage drops; the regulator circuit is to ensure that the switching power supply has a stable output voltage design of. Regulators and standby control circuit not only in the switching power supply in the opposite effect, and the work of the state is the opposite. Standby control circuit work, the regulator circuit does not work; regulator circuit work, the standby control circuit does not work. Regulator circuit and standby control circuit in the switching power supply in this feature determines the two circuits in different working conditions or failure, the switching power supply output voltage. In terms of their working conditions, the standby control circuit VQ822, VQ832 only work in two states: saturation on-state and off-state. Work in saturated conduction state, the switching power supply output voltage drop; work in the off state, the switching power supply output voltage to normal. Therefore, the switching power supply, the standby control circuit failure, only cause the switching power supply output voltage is lower than normal, but will not appear high output voltage failure. Therefore, an effective method of determining whether there is a fault in the standby control circuit when the output voltage of the switching power supply is in a low state is to disconnect the standby control circuit from the circuit. After the standby control circuit is disconnected, the output voltage of the switching power supply is restored to a normal value, You can determine the switching power supply low output voltage fault in the standby control circuit. Maintenance standby control circuit, it should be only VQ832, VQ22, VD836 circuit to check on it. The role of the regulator circuit Since it is the level of the switching power supply output voltage to adjust, and ultimately ensure that the switching power supply output voltage unchanged. Therefore, the switching power supply, the regulator circuit fails, there should be two types of symptoms: First, the switching power supply output voltage high, and second, the output voltage is low. Switching power supply in the high output voltage failure, there are different forms of failure. To sum up, there are several symptoms: (1) switching power supply has a stable, higher than the normal voltage output; (2) the switching power supply is only slightly higher than the normal instantaneous power output voltage output, the output voltage (3) When the switching power supply is in standby mode, it has a voltage output higher than the normal voltage in standby mode, and the output voltage is normal after the standby state is changed to the normal working state; (4) The switching power supply Work in standby mode, the output voltage is normal, the standby state into the normal working condition, the output voltage is higher than normal. Among the four fault phenomena with high output voltage, the fault range of the first and second fault phenomena should be in the common channel circuit of the regulator circuit and the standby control circuit. The voltage regulation circuit and standby control circuit common channel circuit by the NQ838, NQ821 composition, therefore, overhaul the switching power supply has a stable, higher than the normal voltage output and power-on instant higher voltage output, but quickly dropped to "0 "In the event of a fault, the scope of the test should be limited to the NQ838 peripherals and the NQ821. The reasons for the above point of view is: in the switching power supply, NQ838 peripheral circuits and NQ821 under normal circumstances, only the standby control circuit and the sampling circuit components in the case of damage to the case, it will appear switching power supply has a stable, high In the normal voltage output and boot instant higher voltage output, and quickly dropped to "0" fault. In fact, the switching power supply TV standby control circuit and the sampling circuit components in the voltage regulator at the same time the probability of damage is very small, almost impossible in the same circuit, which shows the first and second failure phenomenon in the range of NQ838 peripheral circuits and NQ821. In the switching power supply output voltage high third fault phenomenon, the switching power supply from standby to normal working condition, the output voltage is normal, indicating the switching power supply voltage regulator circuit does not exist fault, which further illustrate the NQ838 peripheral circuits and NQ821 is normal, it is very clear that the cause of the third failure is the standby control circuit failure, overhaul, as long as the standby control circuit consisting of VQ833, VD836 check on the line. For switching power supply output voltage of the fourth failure, it should be said that the performance of the fault form and the third fault manifestation of similarities. As the switching power supply in standby mode, the output voltage is normal, which shows that the standby control circuit and the NQ821, NQ838 composed of the circuit there is no fault in the regulator circuit, if the standby control circuit and NQ821, NQ838 circuit There is no fault, the fault can only be in the sampling circuit of the regulator circuit, so overhauling the fourth fault, only the sampling module NQ833 in the regulator circuit to check on the line. Regulators and standby control circuit failure caused by the second type of fault here do not go into much detail.