KEY BUS TROUBLE isn't a 5820XL message. It doesn't appear in the 5820XL installation manual. The 5820XL talks to its annunciators and expanders over the SBUS, and the manual calls a lost connection there SBUS communication trouble (Page 7-36) [1].

KEY BUS TROUBLE comes from other equipment, so check which screen is showing it:

• Silent Knight SK-5208: the panel has lost communication with a 5235 keypad. Check the SKI and SKO terminals for a short or an open (SK-5208 installation manual, page 7-1).
• Fire-Lite and Notifier LCD annunciators (ANN-80, ANN-100, N-ANN-80): the annunciator shows it on its own screen when the annunciator bus (ANN-BUS) isn't turned on at the panel. Its AC Power light stays off and it beeps about every 10 seconds, but the panel itself shows no trouble. To clear it, turn on the ANN-BUS and program the address that's set on the annunciator (MS-9600LS installation manual, page 50).

If the trouble is on a 5820XL itself, see What does SBUS trouble mean on the 5820XL and how do I resolve it? for the wiring, module ID and power checks.

KEY BUS TROUBLE isn't a 5820XL message. It doesn't appear in the 5820XL installation manual. The 5820XL talks to its annunciators and expanders over the SBUS, and the manual calls a lost connection there SBUS communication trouble (Page 7-36) [1].

KEY BUS TROUBLE comes from other equipment, so check which screen is showing it:

• Silent Knight SK-5208: the panel has lost communication with a 5235 keypad. Check the SKI and SKO terminals for a short or an open (SK-5208 installation manual, page 7-1).
• Fire-Lite and Notifier LCD annunciators (ANN-80, ANN-100, N-ANN-80): the annunciator shows it on its own screen when the annunciator bus (ANN-BUS) isn't turned on at the panel. Its AC Power light stays off and it beeps about every 10 seconds, but the panel itself shows no trouble. To clear it, turn on the ANN-BUS and program the address that's set on the annunciator (MS-9600LS installation manual, page 50).

If the trouble is on a 5820XL itself, see What does SBUS trouble mean on the 5820XL and how do I resolve it? for the wiring, module ID and power checks.