Hi Guys!
I am a beginner in electronics repair. This time I tried to repair an SMPS power supply with 4 outputs 24VDC (10A), 5VDC(10A), 12VDC (4A) and 12VDC (4A) due to intermittent power on/off. After series of checking, I found some few capacitors with high ESR and replaced those with good spares. Now the power is stable and output voltages are all good. But whenever I load test atleast 2A, the voltage drop on outputs 5VDC, 12VDC, 12VDC respectively. The original 5VDC when there is a 2A load becomes 1.3VDC, and the 2 outputs with 12VDC becomes 5.4VDC. However, when I load 8A on 24VDC it drops to 23.6VDC and I think it has no issue. I already have replaced the 2 PWM UC3854BN and all the electrolytic capacitors but still failing. I have removed and measured all the resistors but cannot find abnormal reading. I also have checked the MOSFETs and proactively replaced it with same exact part number. I also have changed the 3-pin voltage reference ICs TL431C but with same result. The problem is I don't have any schematic diagram. Any idea on this is highly appreciated.
PSU Model: PFC375-4200
I am a beginner in electronics repair. This time I tried to repair an SMPS power supply with 4 outputs 24VDC (10A), 5VDC(10A), 12VDC (4A) and 12VDC (4A) due to intermittent power on/off. After series of checking, I found some few capacitors with high ESR and replaced those with good spares. Now the power is stable and output voltages are all good. But whenever I load test atleast 2A, the voltage drop on outputs 5VDC, 12VDC, 12VDC respectively. The original 5VDC when there is a 2A load becomes 1.3VDC, and the 2 outputs with 12VDC becomes 5.4VDC. However, when I load 8A on 24VDC it drops to 23.6VDC and I think it has no issue. I already have replaced the 2 PWM UC3854BN and all the electrolytic capacitors but still failing. I have removed and measured all the resistors but cannot find abnormal reading. I also have checked the MOSFETs and proactively replaced it with same exact part number. I also have changed the 3-pin voltage reference ICs TL431C but with same result. The problem is I don't have any schematic diagram. Any idea on this is highly appreciated.
PSU Model: PFC375-4200
Comment