R&S XU 4200  Visual Inspection 
6166.5368.02.01 4.2   
4.1.2  Checking the LED State 
Introduction 
The LEDs on the front panel of the radio display the status of various 
settings and operating modes. If the LEDs AC, DC, GO or VOP are not 
illuminated, there are a number of possible reasons. 
 
 
 
Fig. 4.1  Checking the LED state. 
 
Indication  Possible cause of fault  Remedy 
LED AC 
not illuminated 
With AC operation only: 
If the secondary voltage of approx. 
28 V is displayed (see chapter 
3.4.7.4.3), LED AC is defective 
 
With AC/DC operation only: 
Mains conne
ctor not plugged in, no 
mains voltage available 
 
Fuse F1 or F2 in AC line input  
defective 
 
Return radio to our service center for 
replacement 
 
 
 
Plug in mains connector X1, check 
mains voltage (see chapter 
3.4.7.4.3) 
Please 
replace the fuses with the 
fuse
s listed in the appendix Fuses. If 
the fuses get defective again after 
the replacement, please send the 
radio to our service center. 
LED DC 
not illuminated 
With AC/DC operation only: 
Battery connector not plugged in or 
no DC voltage available (or reversed 
polarities) 
Fuse F3 in DC line input defective 
 
Plug in battery connector X3 and 
check battery voltage (see chapter 
3.4.7.4.3) 
Please replace the fuses with the 
fuse
s listed in the appendix Fuses. If 
the fuses get defective again after 
the replacement, please send the 
radio to our service center.