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21
SHM-B ASYNC
printed circuit board is properly inserted and fully
seated against the motherboard of the rack.
SYMPTOM: No data transfer in one or both directions
(to, from, or to-and-from the SHM-B).
1. Monitor the TD LED on the sending-end modem
while sending data. The light should flash red/green.
If not, check the DCE/DTE switch on that unit. Once
you get a TD LED flashing on that unit,
simultaneously the RD LED should flash on the other
SHM-B unit. If not, go to step 2.
2. Inspect the wiring between the two modems. Have the
wires been properly installed? Transmit + (TX+) on
one modem must be wired to Receive + (RX+) on the
other modem; also, Transmit - (TX-) must be wired to
Receive - (RX-). Refer to Figure 2 during your
inspection of the four-wire circuit.
3. Try a local test using the Loopback mode (see
Chapter 4). If there is no transfer, check the setting of
S1 and the wiring of your EIA-232 cable.
4. The EIA-232 control signals are at the wrong levels.
Check the EIA-232 interface using a breakout box.