Service manual for Klein & Hummel O 800 subwoofer

[okw]

Hi guys. I'm looking for a service manual for my fathers Klein & Hummel O 800 subwoofer. I get a lot of hits on Google, but need to register my credit card to download. That's not gonna happen Anyone of you have the service manual?
The subwoofer powers up, but there is no sound. He opened the case and looked over it. No loose wires, nothing looks burned (by his eyes), but I'm not with the speaker myself (he lives a few hours away) so I haven't taken any measurements yet. Any clues before I start?