I recently bought a new Zebronics woofer with 4 speakers. It was working fine and one day a voltage spike occured in our area & since then it only works if voume is at its maximum & when volume is turned down then only bass sound comes & treble is like 2 to 3%. I know i can take it to a repair shop but it will be too costly for me. Could someone adivse me how to troubleshoot the issue & replace the damaged part inside it. I can replace the part, I am good at it but i dont know how to trace which part is damaged.

Feel free to ask any query, I will be happy to reply back.
Any suggestion or advise is heartly welcome. Thanx in advance.