On remote press "HOME" > "help & settings" > "system info" > "diagnostics".
The problem is, it has 3 tuners. Make a note of the Tuner 0, 1, & 2 frequencies. Then select a random channel & see which tuner frequency changes. If none of them change then try another random channel, as the first random channel might be on the same frequency as the original channel. Then select the channel you want the frequency for.
You can double check by looking at "Time since tune start" & "Time since signal lock" times.