Are you on cable with the coax cable connected directly to the Philips (Funai) 3506? If that's the case perhaps your cable provider has scrambled all but the local "must carry" sub-channels, public access, governmental, shopping and a few lower interest services. Our local Comcast service had months of on-screen alerts advising customers to obtain their "digital devices" to allow continued reception. There were several mailings with more detailed information. They want customers to spend more $$$ in order to be enslaved to their "digital devices."
If you receive your signal through an antenna then you should run a new "antenna" channel scan as some stations have made changes.
Of course there are other possibilities. I own a Philips 3576 HDD/DVD recorder of February 2008 manufacture. Early on the clear QAM tuner became nearly useless. Following that the 3576 has been set up for ATSC reception where the 3576 functions satisfactory. Another Funai built recorder, a Sylvania ZV450SL8 (from 2007) had the same problems while two similar Magnavox ZV450MW8 and ZV450MW8A models (from 2007 and 2008) have performed well. (I own several other Philips, Magnavox, Pye and Toshiba DVD Recorders--all of them manufactured by Funai.) At the AVS Forum Wajo's threads address many aspects/details of Philips/Funai tuner performance.
All of these matters are discussed in many hundreds, if not thousands of posts at the AVS Forum.