A carpenter brought this battery charger to my shop to be fixed. He told me that sometimes this charger works fine and sometimes it does not. When I powered up the charger, nothing came on and when I checked the output voltage in the battery holder, there was no voltage present there indication a problem in the charger.
I recalled what the man said about the charger sometimes it works and sometimes it does not and I thought to my self, this could be a problem of cold soldering joints or some bad components, in my mind I was thinking capacitors, or it could be both.
I opened the charger and checked with the naked eye to see if there is something bad showing but there was none. I checked with a magnifying lens and I could not see any bad joints. I powered up the charger and checked the voltage on the main capacitor and I got a reading of 300 volts but not steady reading. I traced it back to the main ac outlet connectors and found out that the main AC wire is not in good condition. I replace that wire and tested again. This time I was getting a steady 300 volts on the main capacitor legs but still no indication of any power present beyond the main the primary power section.
I tested with a the LOPT/FBT tester, putting the meter probes one on the main capacitor leg and the other on the collector leg of the MOS N FET (center leg) and I got a full light bar indicating a fully working power section. This means that the main capacitor, the MOS N FET and the secondary diodes are in good operating conditions. I got voltage reading on all the secondary diodes except one diode. There was no reading at all there. When I checked the main operation of this diode, it was the diode responsible for the operation of the charger. When I tested with the LOPT/FBT tester and gave me the indication that all the secondary diodes are work fine, so why I do not have any reading here? Something is pulling the voltage down or the meter is giving me a false reading.
I have worked with this meter for a long time and I trust it fully. I started testing the component connected on the same line of this diode. I saw a capacitor on the same line as this diode and I checked with the ESR meter(GME)and it checked out fine. I thought to my self, what if the meter is giving me the wrong reading. I remember Mr. Jestine Yong talking about this kind of problem in one of his articles on his web site and decided to check the capacitor out and see what is causing this malfunction.
Took the capacitor off the board and checked it and to my surprise, it checked fine again. I checked the capacitor again with the blue ESR meter and this time, it showed no reading on the meter indicating the capacitor is bad. I decided to replace that capacitor. It was 270uf/50 volts. I did not have 270uf to replace it with. I decided to replace it with 330uf/50 volts. To my surprise, the power green led came on flashing which is an indication of a working battery charger. I checked the reading at the battery holder and I got a reading of a 21 steady dc volt there. I was really happy to see that.
I put a battery in the battery holder and the charger recognized it and the green LED flashing light became red steady charging LED. I left the battery there for about an hour and checked it on a power drill and it worked fine.
I trusted my meter for a long time but today I realized that sometimes the meter will work fine but other times it might not. So be ready for this kind of disappointments and get over it.