54
Network Communications—N2 Communications Bus
Communication may fail if one or more of the fuses on the communication
terminal board blows. The TBC801 has six fuses that protect the
components of the NCU/NEU from high voltages and power surges.
(Note that the TBC821, the improved version of the TBC801, uses
thermistors instead of fuses, which provide overload protection and are
also resettable, so that the TBC will work again after it cools off.) The
Fuses F1, F2, and F3 protect TB1; Fuses F4, F5, and F6 protect TB2.
If any of these fuses blows, you need to replace the board.
Table 7: Communication Terminal Board
Terminal Screw
N2 Bus Wire
Fuse
1
N2(+)
F2
2
N2(-)
F1
3
SFT GRD
None
4
REF
F3
5
SFT GRD
None
6
HRD GRD
None
To check the TBC fuses, remove the single screw that holds the board in
place. Pull the board out far enough to enable you to probe the
non-component side of the board. Using an ohmmeter, measure for
continuity across each fuse by first placing one probe on the exposed
portion of the fuse (Figure 32). Place the second probe on the
non-component side of the board, onto the fuse pad with a trace leading
to the ribbon connector.
For example, to test fuse F1, place the probes on the exposed portion of
F1 and to the F1 pad on the non-component side whose trace goes to the
connector. If you measure an open circuit, the fuse is blown.
Checking the
Communication
Terminal Board