I do here plan to accumulate information about the Puxing px‑888k radio I own, that is not covered by the manual. Depending on differences between firmware and/or hardware revisions, the information below may or may not apply to other devices.
To save a frequency to memory 3:
The display will change from RADIO to RADIO S and back.
To to load a frequency from memory 7:
The display will change from RADIO to RADIO L and back, as well as the set frequency to the one stored at memory position 7.
You can not manually lock the device while in broadcast radio mode, since the * button activates the scan-up function. However, the timed auto-lock function remains active if you have enabled it, and it will lock the device after the timeout has been reached. To unlock it again, press and hold * as usual.
This seems to be an edge case in the firmware programming, and probably does not indicate a faulty device. Compare the following:
Make sure the setting LED is set to OFF, then when changing the value of setting LED the display backlight will flicker with the color setting, and the keypad will be briefly lit as well, before both go dark.
Make sure the setting LED is set to AUTO, then when changing the value of setting LED the display backlight will change as the setting changes.
Make sure the setting LED is set to ON the display backlight will flicker with the set color, before going back to the previously stored color.
I own a Cobra microTALK mt725 HT as well, which operates on the PMR466 frequencies and channels, and offers 38 CTCSS settings, although I have been unable to find information on the actual tone frequencies used. This is suboptimal if wanting to pair it with a device like the px‑888k where the CTCSS tones are selected from a list of frequencies in Hz. I have found my Cobra HT to match the following frequencies: