If this is an analog audio LD, the movie soundtrack is probably on the left audio out and the commentary is on the right audio out.
Simply unplug the right audio jack and that should work but the movie soundtrack will only work on the left speaker (unless you put in a Y-Cable to split the audio).
Andendum….
Forgot that this is a Karaoke model. Make sure you have that slide switch on the front panel below the stop button set to “Normal”. If you leave it in “Karaoke” mode, the player automatically chooses the analog audio track and will also pause the disc at the beginning of each chapter. Leaving it in normal allows the player to just be an LD player for movies and default to the digital audio tracks.
Lastly, you should look for a remote for this unit if you want to fully utilize the player. You don’t need the exact remote but just one w/ the basic functions. Here are examples…
This one lacks the key changer buttons and power but actually has more functions than the original remote (e.g.: A - B Repeat and Multi Speed)
https://www.ebay.com/itm/Genuine-Pionee ... 632-2357-0This one is for a CLD-V820 which is the both side play model. Basically the same remote as the 720 but w/ side change buttons
https://www.ebay.com/itm/PIONEER-CU-CLD ... 632-2357-0This might be the exact remote for a 720 but I’m not 100% certain
https://www.ebay.com/itm/Pioneer-LaserD ... 632-2357-0