66 THE BLUE BOX LT TROUBLESHOOTING WITH AN OSCILLOSCOPE
LCDBBTSWO03Sept08
Bus Checker Card
Bus Checker Card
Bus Checker Card
Data/Power Jumper
Data/Power Jumper
Data/Power Jumper
BUS SPLITTING TECHNIqUE
!
Note:To speed up troubleshooting when readings are
less than 200Ω on the Continuity or Short-Circuit test,
refer to the “Bus Length Chart” on page 4 before splitting
the bus; this can provide an approximate distance to a
shorted pair or extra terminator from the test point.
On the middle device of the bus, disconnect one Cat. 1.
5 cable to create two smaller “half-buses”.
Test each “half-bus” to find the side with the out-of-2.
range values.
Repeat steps 1 & 2 on the out-of-range “half-bus,” 3.
to create another “half-bus” until the cable, crimp or
device creating the out of range measurements is lo-
cated.
The idea is to split a bus in half and then half again – over
and over until the bad area has been located. It is also OK
to visually inspect each cable, crimp or device to detect the
problem.