Hi. I'm stuck on a repair for an FBT Promax 10a.
I have tried changing the output transistors, i replaced with 4 identical but originals have slightly different markings on one of the transistors, i don't think it's relevant the main number is the same IRF B5620.
I swapped the input boards between the two speakers so thats not the issue.
PSU seems fine.
Looks like the fault is in the pre drive stage of the main board.
Any ideas?
Also i found this that might be useful to some people.
TIP. regarding a screw that grounds input board to main board on fbt promax 10a (if the screw with bronze spacer is missing or loose the protection will cut in, might be same on 14a).