If this speaker is not powered anymore, it is probably caused by faulty components in the power supply. I repaired this unit for one of my customers. I found 4 primary filter elco’s (all in parallel) that were completely decayed. These parts were oxidized and some of them had broken leads. Further the bridge rectifier (KBP206G) and a 3.15A fuse were blown. I replaced all the parts and used some very good quality capacitors. Use the same dimensions for the capacitors by the way, otherwise you cannot close the metal case afterwards. I also replaced an NTC preventively. After placing all the parts back, the speaker was repaired and produced some great sound again.
The most difficult part of the repair is opening the case. You first have to get the black aluminum front plate off from the speaker case. You need some hot air to soften the glue and pull very carefully. When the plate is completely removed, unscrew the woofer from the case and carefully disconnect the wires. You should use gloves at this point, because there is a lot of dirty and sticky foam around the wires. After removing the woofer, unscrew the black plate where the tweeters are mounted and carefully lift it up and disconnect the necessary wires until you can lift it completely out of the case. From there, you can disassemble the metal case where the power supply is built in.
You can also find a video on Youtube where you can see how to disassemble this speaker.
Don’t hesitate to contact me if you have any questions about this repair.