Overhaul of STR-F6454 Switching Power Supply
STR-F6454STR-F6454 is a special thick film circuit for switching power supply produced by Sanken, containing oscillation circuit, over-current, over-voltage, voltage regulator control and switching pulse amplification circuits. The thick film block in Changhong CN-11 movement colour TV (H25K6O, 25Kl8, 29Kl9, C-29E6 and other models) in the application of the circuit shown in Figure. The overhaul steps for this movement colour TV repeatedly burning STR-F6454 are as follows:
1. Check the rectifier filter circuit if the fuse is blackened and STR-F6454 (NQB21) is blown up and damaged, you should check the rectifier diode VD801A~VD8O4A, surge absorbing capacitor C805~C808, +300V filtering capacitor C810, spike absorbing capacitor C811, C827 (some models do not have C827, R823, R824, UB822). UB822).
2. Check STR-F6454 (4) feet external circuit STR-F6454 (4) feet for the power supply start-up power supply, the normal voltage is 18.2 V. If the foot of the voltage is less than 11 V and stable, then check the V801, VD808 (l8V), VD803 (22V) and other components as the core of the electronic voltage regulator circuit; if the fluctuations between lllV ~ l5V, that the Switching power supply has been vibration, then check the switching transformer secondary rectifier, filtering components and load circuits with or without short-circuit phenomenon, especially the line circuit.
3. Check the voltage regulator control loop if the power-on moment +B voltage from 160V gradually declined to zero, then check the voltage regulator control loop components, you can replace the optocoupler N830, and then change the error amplifier N831, it is best to check whether the R807 is open-circuit.
Tip: the IC's (4), (5) feet between the external Schottky diode AKO3. repair may not be installed in this diode, or replaced with RU2, RU4, 55295 and other types of diodes.
