The RTL8192S has two antennas. If the driver selects a dead antenna, you see 0% signal.
The community realized that the RTL8192S is almost identical to the RTL8192SU (USB variant). A driver called rtl8192su (from staging) works if you modify USB IDs. rtl8192s wlan adapter driver work
Workaround: Force the r8712u driver (for RTL8192SU) with the RTL8192S VID/PID. It is not perfect (LEDs act weird, no 40 MHz channels), but it works. The RTL8192S has two antennas
The driver does not implement the full 802.11 protocol stack. Instead, it registers as a "hardware driver" with mac80211. The driver must implement a set of callback operations, defined in the ieee80211_ops structure. These callbacks include: no 40 MHz channels)