If you have not done a reset to factory settings after installing the new operating system Android Lollipop on your Samsung Galaxy S5, it can happen that your saved Bluetooth devices cannot be detected or may not connect. If you have any problems with the Bluetooth connection after the update unfortunately only the following method helps besides a factory reset:
Delete the stored connected Bluetooth devices onto your Samsung Galaxy S5.
Loosen the couplings in Menu --> Bluetooth -> Preferences and then connect your Samsung Galaxy S5 again with the Bluetooth device. This will cause the Bluetooth connection settings that have been disturbed by the update to Android Lollipop work perfectly again and a connection is established.
You now know what you can do without a factory reset, so that your Samsung Galaxy S5 with Android Lollipop connects again properly to already paired Bluetooth devices.
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