I knew I was going to have to type fast to beat ICE on responding to this.
One other thing that's possible.
Both the G14 and G18 music are ZK, and on G14 the still video display for the music are also ZK, however the images on MY 4200 just blink on for a fraction of a second, and most of the time the screen is blank (whereas if I play from my GENPIX to VLC, the images are constant. So it's possible that you might get a predominantly blank screen. You should still get audio though, except that sometimes the 4200 will start up in an undefined audio mode. I forget the menu item, but it's in one of the first two menus, where there is an audio/video setup. You might try changing the audio "language" then go back to English. I've had times when I got no audio until I did that. That plus a blank screen might make you think you weren't getting the channel.
I'm also curious what firmware version you have? (it's near the top in diagnostic A.
EDIT: related to the firmware version, it MIGHT help if you could get the receiver to receive a firmware update, IF you can find a DCII signal that's giving firmware. I would recommend some time that you're not doing anything, lock in the Nebraska PBS signal on G28. Just leave it there for a while, particularly over the weekend, and watch diagnostic screen A. If by chance they are uploading new firmware, the numbers in the row that shows the firmware about 4 times should change indicating that it's found new firmware. It will start downloading automatically, and the download takes about 10 minutes if I remember right. I THINK that the newer firmware was specifically designed for FTA'ers. The original firmware was semi FTA friendly, but then they came out with firmware that made boat anchors out of the receivers, so GI made a special version that was FTA friendly. Perhaps this version would work better, however finding an uplink that has the firmware is not real likely, but it's possible. I really think that NET is the most likely place to find it, since they are uplinking to multiple sites around the state, some of which may still have 4200s.