Garmin SL40 Comm question

Does the Garmin SL40 have a setting other than the push buttom that allows or not the use of monitoring stand by frequency?

The function worked for a few months when i was doing flight testing then one day it stop working. I cant find anything on the manual about that. Thanks for any help.

Don't remember a setting, but thought there was a pin to allow monitoring via an external push button.

Larry