The AC-DC-AC Inverter Solved

This is a local brand  AC- DC- AC INVERTER  that has the ability to convert 12 volt car battery to 220 VAC. It can also charge the car battery with 220 AC.

This machine is good either for charging the battery of car as well as to use it as a source of 220 Ac in places that no electricity is available like sea sides or mountains and out-doors places and etc. The problem of this inverter was after many years of services, it stopped to work and want to be retired. With no diagram available, I started to repair it after opening the cover:

I found many cold solder joints  and believe this could be the problem. So I resoldered all the dry joints. After done the resoldering work, I started to turn On this device but unfortunately this device refuse to work. I proceeded to check all the transistors and still could not locate any bad transistors on the board either !

Then  next step was to check on all electrolytic  capacitors in the circuit board. I found five bad small caps out of the range with high ESR caps. Some have low capacitance like 10 micro farad 16 volt and 10 micro with 100 volts. The big none polarized cap 0.07 micro 1000 volts that is in series with AC input line checked to be good but ESR value showed open circuit. I replaced this one as well but the device still refuse to work.

This device has a big transformer with 6 big power transistors 2n3055 that converting the 12 volt DC of car battery to 220 AC and one smaller transformer and all were tested good too.

The next test was the relay (HH54S) and when I pumped in the external 12 volt dc to check it, it seems that it was totally dead and no sign of life. I replaced the relay and the device started to work again.

Conclusion: This device had multiple problems:

1-Bad soldering joints

2-Bad caps with high ESR value and

3-A bad relay