Kramer Electronics VM-1042 - Manual (Page 21)

KRAMER ELECTRONICS LTD.
19
Problem Remedy
Noise bars "roll"
up or down in the
output image
or:
Low frequency
hum in the output
signal
Hum bars (ground loop) are caused by a difference in the ground potential of any
two or more devices connected to your signal path. This voltage difference passes
through any available interconnection, including your video cables.
WARNING !
Do not disconnect the ground from any piece of video
equipment in your signal path!
Check the following to remove hum bars:
1. Confirm that all interconnected equipment is connected to the same
phase of power, if possible.
2. Remove equipment connected to the phase that may be introducing
noise, such as motors, generators, etc.
3. Disconnect all cables and reconnect them one at a time until ground loop
reappears. Disconnect the affected cable and replace, or insert an
isolation device (opto isolator or transformer) in the signal path.