Looking for the access codes for Zenith z50pv220, which, I think, is a re-branded version (with reduced features) of LG 50PV450.
I have tried keeping the "Menu' button on the TV itself, as well as on the remote, (and both at the same too), without any success.
edit: I did find the "Host Diagnostic" screen to investigate the signal quality of a problem channel.
1) Place Television on the digital channel that may be showing problem.
2) Bring up the Menu. Highlight “CHANNEL”. Press “ENTER” on the remote.
4) Press the (1) Key 5 to 8 times.
The Host Diagnostics screen appears.
This screen shows the Model #, Firmware version, and DTV SNR (Digital Television Signal to Noise Ratio)
Over the Air: 8VSB Above 20 is good
Cable Digital: QAM64 (Above 24 is good)
Cable Digital: QAM 256 (Above 30 is good)