Press and hold [Vol+] + [Info] on front panel simultaneously for ~10 seconds, then release
or...
Press and hold [Select] for ~10 seconds, then release and press [Up]:
Info/Settings available here:
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RF Levels
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HDMI/EDID information
-
Activate AC3/DD Support over HDMI
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Factory Reset
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Internal/External HDD Reformat
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STB Reboot
-
CCI Status for current program (digital content protection - Copy Freely, Copy Once, etc.)
-
much much more...
I switched to a live channel for the next few otherwise no pertinent audio and video parameters were displayed:
Note spelling error - "Resolustion" - hope the rest of the code was proofread better than that!

The "AC3 in Host" Flag shown below changed to "Support" after "AC3 over HDMI" was enabled:
A little better screen formatting needed here:
This page was password protected... was able to enable AC3 over HDMI here...
Curious what "Enable Allow NC HDMI TV" actually does (did not change setting):
Another password protected screen:
It's more like 30 seconds... thought the reboot function wasn't working at first:
There are many many more screens... these were the most interesting. In particular there are a bunch of CableCard related screens that I did not post (but the main CableCard MMI menu is shown above).