Maintenance steps for regulated power supply
Maintenance steps for regulated power supply
1. When repairing a switching power supply, first use a multimeter to check whether each power component has a breakdown or short circuit,
Switch power supply housing
Such as power rectifier bridge stack, switch tube, high-frequency high-power rectifier tube; Is the high-power resistor that suppresses surge current burnt out. Check if the resistance of each output voltage port is abnormal again. If the above components are damaged, they need to be replaced.
2. After the first step is completed, if the power supply is turned on and it still cannot work properly, then the power factor module (PFC) and pulse width modulation component (PWM) should be tested, relevant information should be consulted, and the functions of each pin of the PFC and PWM modules and the necessary conditions for their normal operation should be familiarized.
3. Then, for the power supply with PFC circuit, it is necessary to measure whether the voltage at both ends of the filter capacitor is about 380VDC. If there is a voltage of about 380VDC, it means that the PFC module is working normally. Then, it is necessary to detect the working state of the PWM module, measure its power input terminal VC, reference voltage output terminal VR, start and control the Vstart/Vcontrol terminal voltage, and use 220VAC/220VAC isolation transformer to supply power to the switching power supply, Use an oscilloscope to observe whether the waveform of PWM module CT end to ground is Sawtooth wave wave or triangle wave with good linearity. For example, TL494 CT end is Sawtooth wave wave, and FA5310 CT end is triangle wave. Is the waveform of output V0 an ordered narrow pulse signal.
Maintenance steps for regulated power supply
4. In the maintenance practice of switch power supplies, many switch power supplies use UC38 ×× Series 8-pin PWM components,
ACDC Adapte
Most power supplies do not work because the startup resistance of the power supply is damaged or the performance of the chip decreases. When there is no VC after the R circuit is broken, the PWM component cannot work and needs to be replaced with a resistor with the same power resistance value as the original one. When the starting current of the PWM component increases, the R value can be reduced until the PWM component can operate normally. When repairing a GE DR power supply, the PWM module was UC3843, and no other abnormalities were detected. After connecting a 220K resistor to R (220K), the PWM component worked and the output voltage was normal. Sometimes, due to peripheral circuit faults, the 5V voltage at the VR end is 0V, and the PWM component does not work. When repairing the power supply of the Kodak 8900 camera, this situation is encountered. The external circuit connected to the VR end is disconnected, and the VR changes from 0V to 5V. The PWM component operates normally and the output voltage is normal.
5. When there is no voltage of around 380VDC on the filter capacitor, it indicates that the PFC circuit is not working properly,
Maintenance steps for regulated power supply
Schematic diagram of switch power supply circuit
The key detection pins of the PFC module are the power input pin VC, the start pin Vstart/control, the CT and RT pins, and the V0 pin. When repairing a Fuji 3000 camera, test that there is no 380VDC voltage on the filter capacitor on one board. VC, Vstart/control, CT, RT waveforms, and V0 waveforms are all normal, but there is no V0 waveform at the G-pole of the measured field-effect power switch due to FA5331 (PFC)
