Black Box IC476A-F-R2 - Manual (Page 24)

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APPENDIX C: Self-Test
1) To perform a self-test/functionality test of the units, set the 8-position
DIP switch for 4W point-to-point operation (see the chart in
Section 3.2.2
).
2) Using two short pieces of twisted-pair cable, connect one wire between
XMT+ and RCV+. Connect the other wire between XMT- and RCV-.
3) Send data from the RS-232 device. Whatever you send out you should
receive back.
4) If you receive nothing back...
a) there’s not enough (or any) power to the Converter. The
Converter requires at least 6 VDC under load. Or,
b) one or both of the twisted-pair cables is bad. Or,
c) the Converter’s DTE/DCE switch is in the wrong position. Or,
d) the Converter is defective.
5) If you receive the data back but it is garbled, flip the + and - connections
on the RCV connection. If that does not resolve the problem, make sure
that sufficient voltage is being supplied by the RS-232 interface (see 4a,
above).
6) If you receive back what you sent, the Converter is working properly.
Appendix C. Self-Test