Lighting Controls Blue Box LT Series Installation, Operation & Maintenance Manual page 65

THE BLUE BOX LT TROUBLESHOOTING WITH AN OSCILLOSCOPE
USING AN OSCILLOSCOPE TO TEST
A DIGITAL BUS (Continued)
6 . With a partially bad device, it is sometimes hard to
distinguish because it looks very similar to a good bus .
One has to carefully examine the waveform and see
if the baseline is centered at Zero .
7 . A bad device causes the baseline to shift and become
unbalanced . (Baseline is not at Zero anymore) . Below
are three examples where A & B are not equal .
8 . Use the Bus-Splitting technique to find the problem .
Problematic: Ringing on peak of square wave means the bus
is missing one or both terminators. +V = -V means no bad
devices.
Problematic: Clean square waves mean the bus is termi-
nated. But +V ≠ -V means damaged devices. Usually caused
by over-voltage: static, lightning, or line voltage.
Problematic: Ringing and dampened square wave means
that the bus is missing one or both terminators. +V ≠ -V
means damaged devices. Usually caused by over-voltage:
static, lightning, or line voltage.
+V = -V
Problematic: Ringing and extremely dampened square wave
means the bus is missing one or both terminators. +V ≠
-V means damaged devices. Usually caused by over-voltage:
static, lightning, or line voltage.
+V ≠ -V
65
+V ≠ -V
+V ≠ -V