Shorted E-cap In Appex SMPS Repaired
This APPEX SMPS Model: LC-8360BTX was brought to me and the complaint was it had been connected into the 220 volt outlet with the back Voltage Selector in the position of 110 volt.
Wow! The paper seal of the manufacturer had not been violated yet, in other words, I was the first person in opening this PSU.
The unit was dismantled, a piece of cake, only four screws in the upper cover:
As you can see in the photos above the PCB was very dirty, of course it was cleaned quickly for having a better access to the circuitry. Of course that the fuse was blown, right away the four diodes were tested with the Digital Multimeter and they were ok too. The oscillator transistors (MJE13007 in this specific case) were checked on as fine too. All the e-caps of the primary side were checked with the Blue ESR Meter/Cap meter and they were ok too, such as the resistors, some other diodes and etc., etc. But in the secondary side, found an e-cap (1000µF/16v) in bad conditions, it was substituted. If you want to learn how to repair SMPS you can check out the Ebook by Jestine Yong.
On the other hand many cold solder joints were found too.
Of course I won’t show more photos because they were a great deal of them. All these cold solder joints were repaired with fresh tin. After all this, the SMPS was connected into 110 volt outlet, but this time with the incandescent bulb and look at the result in the photo below:
Obviously there was still a short-circuit in the circuit board, and I had tested all the components in the primary side. It got to be something shorted that had caused the light bulb to lights up. From my experience, the two big filter capacitors (470µF/200v) can be tested good using any ESR meter and Digital Capacitor meter but can fail when under load. This means when full voltage is applied to the capacitor, the bad capacitor internal plate can go shorted causing the bulb to lights up. This is a not a common case as most of the capacitor problem are due to bad ESR and capacitance value run. If I have the insulation tester I will be able to test out which one is the culprit. I just tested one by one and found one of it bad.
I started to look for the parts from my junk board and found the e-caps.
I directly replaced the two capacitors even though only found one to have problem. They were soldered into the circuit and look what happened when the SMPS was connected into the AC-mains.
This time there was no danger of short-circuit, so the bulb was de-soldered from the PCB, the fuse was substituted for a good one and when the SMPS was switched on look at the result in the photos below:
Only one thing I want to express: another device saved from the junk.
This article was prepared for you by Humberto Rodriguez, one of our ‘Master Authors’ from Cuba.
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