A friend bought this amp but didn’t do anything when plugged in.
Opened to find out the power board wire jumpers were cut from the preamp board inside. That would explain it. Apparently this is done so it can be powered externally from another device, and used just as a preamp, or split the preamp and power amp sections (however the power side did not have the socket fitted).
Customer wanted to just restore to original all-in-one, so the wire jumpers were replaced:
Powers up normally and all good again 🙂
Quick fix nothing else needed!