Bypassing AG-1980 DNR
 

Is this possible? I am wondering if there is a way to simply bypass whatever is applying the DNR and only apply the TBC.

Nope. The panel buttons that look like DNR on/off buttons were never programmed. They don't do a thing. People in video and user forums have known this for years. Panasonic made non-tbc/non-dnr SVHS machines that are similar to the 1980's output but without the dnr/tbc. The PV-S46xx series and AG Pro VCR's from 1995-1996 are the best models. Anything made after 1996 except for a couple of AGs like the 1980 are trash. I own a PV-S4670 and PV-S4672 whose output looks pretty much like the 1980 but with no tbc or dnr. Often a tape will play with a less "enhanced" picture than it does on my 1980. It all depends on the tape.

For those non-tbc machines I use a DVD pass-thru device for tbc, either my Panasonic or Toshiba, again depending on the tape. Toshiba has the weaker tbc but much cleaner color. Some tapes track so well on the 4600's I sometimes can't tell if a tbc is doing anything unless I look at the borders or a test tape.