I picked up this KS900.6 from the classifieds a few months ago and when I went to install it this weekend I found that one of the gain knobs had come out of its socket and was loose inside the chassis. I took a few gut shots while I had the skirt popped to retrieve it.
These amps have been out for years and gut shots probably exist elsewhere, but whatever.
Sorry I don't have the macro photography skills typically seen in these type of threads. I do have several more closeups if anyone is looking at something in particular. Don't ask me questions, I don't know amp design.
I have the 900.6 with the same problem, am not using it now though. It was the front left gain control on my amp that come disconnected from the inside of the amp. Great amp though.