What is the maintenance method for STR-F6454 switching power supply
STR-F6454STR-F6454 is a thick film circuit specifically designed for switching power supplies produced by Sanken Company, which includes oscillation circuits, overcurrent, overvoltage, voltage stabilization control, and switch pulse amplification circuits. The application circuit of this thick film block in Changhong CN-11 movement color televisions (H25K6O, 25Kl8, 29Kl9, C-29E6 and other models) is shown in the figure. The maintenance steps for the STR-F6454 repeatedly burning on the movement color TV are as follows:
1. Check the rectification and filtering circuit. If the fuse is black and STR-F6454 (NQB21) is damaged due to explosion, check the rectification diodes VD801A~VD8O4A, surge absorption capacitors C805~C808,+300V filtering capacitors C810, peak absorption capacitors C811, C827 (some models do not have C827, R823, R824, UB822).
2. Check the external circuit of STR-F6454 (4) pin. STR-F6454 (4) pin is the power start supply terminal, and the normal voltage is 18.2V. If the voltage of the pin is less than 11V and remains stable, check the electronic voltage regulator circuit with V801, VD808 (l8V), VD803 (22V) and other components as the core; If it fluctuates between llV and l5V, it indicates that the switching power supply has started to vibrate. Check for short circuits in the secondary rectification, filtering components, and load circuits of the switching transformer, especially in the line circuit.
3. Check the voltage regulator control loop. If the+B voltage gradually drops from 160V to zero at the moment of power on, check the components of the voltage regulator control loop. You can first replace the optocoupler N830 and then replace the error amplifier N831. It is best to check if R807 is open circuit.
Tip: The (4) and (5) pins of this IC are externally connected with a Schottky diode AKO3. During actual repair, this diode may not be installed or replaced with RU2, RU4, 55295 and other types of diodes.
