This is an active sound reinforcement system that was brought to my shop with the problem of no power in the amplifier. This speaker system was used under a heavy load causing the amplifier to shut down and not working again.
When opening the back cover and took the main board power out, I realized the main fuse was blown and it was dark indicating a heavy short in the board.
I took the fuse out and replace it with a 100 watt light bulb and sure enough, the light bulb showed a heavy short in there because when connected the light bulb to the fuse terminals, the light came on really bright and stayed bright.
The first thing I suspected was the main bridge rectifier; there were two of them on that board. Soldered them off board and checked them and both checked fine. My thoughts were shifted directly to the power transistors in the amplification section of the board. Upon checking the transistors there, I found a D1047, B817 and IRFP150N that gone bad. Two transistors and one MOS N FET. When checking them with my digital meter, all of these parts where shorted out which explain the main blown fuse. All these parts were found left channel of the amplifier, the right channel was working ok.
I had no problem finding the two transistors in the market but the IRFP150N was hard to find since it was built with high ampere. It was 39 ampere, 140 watts, and only 100 volts. I had to go a special place that deals with amplifiers, speakers and sound systems. Finally, found the part and soldered them on board. I did not want to risk the new parts, so I tried the light bulb trick again. When connected the light blub to the main fuse terminals, the light came on very bright and then it dimmed down to no light. That brought a big smile on my face. I am now sure, the short in this board is gone and it is safe now to put the 4 ampere fuse back and try it out.
I plugged the main speaker back to the board and fired up the amplifier, the power light came on steady and I could hear the sound in the speaker loud and clear.