Many thanks to SWLing Post contributor, John Carrod, who writes:
I took delivery of my PL-880 and have seen your notes on hidden features.
With the radio off, press and hold button 5, this disables/enables the light switch.
Pressing same button whilst on FM reveals information of which I’m unsure, I expect you or your readers will no doubt know what that’s about.
Thanks for sharing this, John. I’ve let a friend borrow my PL-880 so I don’t have it for reference. I’m hoping someone here can shed some light on the information display you’re seeing by pressing button 5 while in FM mode.
FM de-emphasis…
De-emphasis means attenuating those frequencies by the amount by which they are boosted. The purpose is to improve the signal-to-noise ratio for FM reception.
“Pressing same button whilst on FM reveals information of which I’m unsure, I expect you or your readers will no doubt know what that’s about.”
This appears to be an FM audio de-emphasis setting. 75 microseconds is a North American standard while 50 microseconds is a European standard. Pressing button 5 repeatedly switches between 75 and 50.
More info here:
https://www.fmsystems-inc.com/audio-de-emphasis-response-table/
The pressing 5 while in FM-mode alters the de-emphasis between 50 µs (for European FM broadcast) and 75 µs (for FM broadcast in the USA).
When I push the 5 button on FM 50.US flashes up. When I push it again 75.US flashes up. Then 50.US etc.
I’ve no idea what that refers to!