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Green Power BP430A – ATX PC Power Supply Repaired
This pc power supply was completely dead and with electronic knowledge that I received from this eBook: TROUBLE SHOOTING AND REPAIRING Switch Mode Power Supply ( by: MR Jestine Yong) I started to repair it.
After opening the unit and blowing off the dusts, I found 5 electrolytic caps that were bulged. From the picture the electrolyte liquid were boiled inside the cap due to heat and then came on the top and dried there.
There were many cold solder joints in the PCB board. The bridge rectifier and fuse were good
In the above picture, the solder joints could only be resoldered with the help of flux liquid.
(Special thanks to MR Jestine YONG for good suggestions)
I also found 6 Toroidal coils/inductors that were good. Two were installed at the AC supply input area and the other 4 were at the secondary side (DC output).
At secondary side of SMPS, I found one of the 4 Schottky diodes SBR 4060 PT (60 VOLT 40 Amp) was shorted when tested with analog Multimeter set to X 10 K ohm
This Power supply unit has three SMPS transformer for 5+ 12+ 3.3+ volt and all were tested good with my blue ring tester
The control IC TL494CN was found to be good after tested the output signal (square wave) with an oscilloscope.
Then I perform a test with 100 watt bulb . First I removed the fuse, solder the light bulb wires across the fuse terminal then connect the terminals to the ATX power supply tester. After plug in the power supply the light bulb first started to glow then became very dim
As you can see all the voltages more or less the same except stand by +5 volt (5VSB) that is 5.8 volt which is more than the rated value (4.75-5.25 volts).Then I removed the bulb and reinstalled the fuse.
I started to check backward from the terminal of 5 +volt (purple wire) to the board. I found another big Schottky diode. SB540 is a 40 volt 5 ampere diode. It was tested good with analog meter set to x 10 K ohm.
IC PS 223
This IC controls the over voltages and under voltages of all outputs and checked to be good. At the nearby area of this IC I found three electrolytic caps to be bad.
1- 10@ 50 volt were tested by ESR METER and it showed open circuit (no ESR value) and capacitance tester showed that it was only 1.5 microfarad.
2- 1 micro farad @ 50 volts also has high ESR value.
I changed all the bad e-caps and the 5 volt stand by voltage was back to normal.
This article was prepared for you by Mr Beh, one of our ‘Master Authors’ from Iran.
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