Service
Service
23
Service
Measuring points
TwinBus power supply unit 1 7573
TwinBus door intercom module 1 4760 / TwinBus built-in loudspeaker 1 4921
TwinBus indoor telephone and indoor video station
Thermal fuses
Instead of conventional fuses, power supply units 1 7573, 1 4874, 1 6371 and mains transformers 1 6476, 1 6477
have electronic fuses that interrupt the relevant circuit in the event of an overload.
If one of these fuses is tripped, the associated voltage indicator LED in the power supply unit goes off. Proceed as
follows to switch on again:
➤
Switch mains voltage off and leave off for approximately 1 minute.
➤
Remedy short circuit or overload.
➤
Switch mains power supply on again.
The associated voltage indicator LED in the power supply unit is lit again.
Mains transformers do not have any LED to act as voltage indicator.
Clamp
Load
Target voltage
a1
b
open/switched
24 V DC to 30 V DC
a2
b
open/switched
24 V DC to 30 V DC
a3
b
open/switched
24 V DC to 30 V DC
1
b
no door communication
0 V DC
1
b
with door communication
24 V DC
2
b
no door communication
30 V DC
2
b
with door communication
0 V DC
3
4
without load
11 V AC
Clamp
Target voltage
2
1
no door communication
15 V DC or 30 V DC
1
2
with door communication
24 V DC
3
4
11 V AC
Clamp
Target voltage
a
b
20 V DC to 28 V DC
ED
ED
20 V DC to 28 V DC
~
~
AC 16 V or DC 18 V
V
a
V
b
< 1 V
