20 Most Recent KLH R5000 5.1 Dolby Digital Surround Receiver - Page 6 Questions & Answers

one channel will not record

Most likely a cable problem - that hum is likely 60hz hum from an improper ground connection. The cable between the sub and the amp needs to be checked and repaired or replaced.

This woofer was taken from a KLH Pro-71 Series. These were the top of the KLH line from ~94-99 when it was still a real company and not just a name. The woofer is rated for 5-350 watts at 8 ohms. Source: KLH Pro Series-71 Spec Sheet.

This happens because the signal received by the laser sensor in the optical head is too low to be decoded reliably. This is caused either by a dirtly lens - clean it with something like this
http://www.amazon.co.uk/Hama-DVD-Laser-Cleaning-Disc/dp/B00005UPDF
or by a failing laser diode. If the cleaning fails to improve the situation then the diode is surely to blame. The only way to fix that is to replace the entire optical mechanism. That is going to be very costly so you must decide if it won't be more cost effective to just get a new unit.

How do we knwo it has a good input? The problem could be higher up the food chain. Plug a known good audio source into it. Any Line Level source will do.