Problem: 

An entrance station will not go into programming mode. Depending on the model, the procedure for going into programming mode will vary. On a station that is behaving normally, an in-use light will blink for several seconds before going solid. If a long error code is heard instead, either as soon as the button is pressed or after a few moments, programming mode cannot be entered. Sometimes, there can be no signs of life on the entrance panel at all.

Possible Causes and Tests:

1. Another entrance station on the system is set to the same ID. Power down the system and double check the dip switches on the panels. Make adjustments and power up the system again. See the appropriate manual for the station to check which dip switches control the station's ID.
2. Low or no voltage going to the speaker module, or a working GT-BC with a power supply is not connected. 
   1. Verify that the R1/R2 wires that go into the speaker module on the entrance station are showing 24V DC. 
   2. If there is no or low voltage, check the GT-BC. Verify that the GT-BC is connected to the entrance station, has a 24V DC power supply (Aiphone PS-2420UL is preferred), and shows a solid status light.
   3. If it does, take the speaker module and connect it to the GT-BC bus controller directly. Attempt to go into programming mode when directly connected. If it does, check the wiring going to the entrance station.
   4. If the light on the GT-BC is flickering or it is emitting a clicking sound, that can be a sign of a short somewhere in the system. Power down the GT-BC, disconnect the R1/R2 wires from it, and power it back on. If the flickering and clicking continues, that can be a sign of electrical damage. If it does not, reconnect R1/R2 cables to the GT-BC's distribution point while powered down one at a time to locate the source of the short.