How to debug remote over HDMI not working

I have a Pi3 connected via HDMI to a Panasonic TH-42PX600A
When Rasplex starts the TV automatically switches its source to HDMI1, when the Rasplex is shutdown the TV is automatically turned off.
The TV settings indicate that HDMI control is on and the above would appear to indicate that the cable supports control over HDMI and that it is working, to some extent.
However, none of the buttons on the Panasonic remote have any effect on the Rasplex.
Are there some diagnositics/logs I can turn on and examine to work out what is going on here?
Thanks,
Mark

you might want to check this thread

Looks like my TV is a bit ‘too old’, all that the logs get is when I change input sources, like this
05:17:12 T:1850733536 DEBUG: CecLogMessage - >> 04:83
05:17:12 T:1850733536 DEBUG: CecLogMessage - << Playback 1 (4) -> broadcast (F): physical address 1000
05:17:12 T:1850733536 DEBUG: CecLogMessage - << 4f:84:10:00:04
05:17:12 T:1850733536 DEBUG: CecLogMessage - >> TV (0) -> Playback 1 (4): give physical address (83)
Remote button presses yield nothing at all.
Thought there might be something in the ‘sevice mode’ TV menus, but I can’t even find out how to get into that, so far all I’ve found is a code to do a ‘factory reset’.
Any idea if it is worth trying to go further down this path?

well it could be the HDMI cable that doesnt support cec and not the fault of your TV

personally I never bothered with cec and used a wiimote as my remote

Do you have a pointer to how to get the wiimote working?
Everything I can find seems to revolve around python scripts and/or dongles (which should not be needed for the Pi3)

I made this script for that

of course there are other remote solutions you can try