I use Comcast (in SE CT). But the channel allocations (here) are (no doubt) different in other local (Comcast) ISP hubs.
Here, CPTV has it's low band (over air/ NON-HD) feed on ch-16. The HD feed is on ch-24.1 But that (ch) will show up (be received) differently on different TVs because there are lotsa different (types of internal digital) tuners in them.
I would scan your channels (click the ch-button sequentially up) until you see the (same PBS) program on another channel. If you can't find it, do a "re-programming" sequence in your "set up" menu -- it could be that newer channels (allocations / multiplexing) were added or changed since the time your tuner initially (last) programmed itself.
Of course, the HD feed (ch) will only be HD quality, if it's recorded (& broadcast) in HD. LOL. Luckily TV is going, more & more, in that direction.