Teledyne 300M - Manual (Page 122)

Teledyne API Model 300M CO Analyzer Instruction Manual, 04033, Rev. A
The modem is configured as Data Communications Equipment (DCE), and may have
additional signal requirements to enable transmission. See modem troubleshooting
section below.
NOTE
MODEMS ARE ESPECIALLY DIFFICULT BECAUSE THEY MAY
HAVE PINS THAT NEED TO BE AT CERTAIN EIA RS-232 LEVELS
BEFORE THE MODEM WILL TRANSMIT DATA. THE MOST
COMMON REQUIREMENT IS THE READY TO SEND (RTS) SIGNAL
MUST BE AT LOGIC HIGH (+5V TO +15V) BEFORE THE MODEM
WILL TRANSMIT.
THE TELEDYNE API ANALYZER SETS PIN 8 (RTS) TO 10 VOLTS TO
ENABLE MODEM TRANSMISSION.
Troubleshooting the modem connection:
First: Disconnect the RS-232 cable from the analyzer and verify (use a DVM) that you
are getting a signal on Pin 2 of the RS232 port on the analyzer. The signal will be
between -5V and -15V with respect to signal ground (pin 5). If not, there is a problem
with the CPU board or the cable. This is the transmit (TD) signal out of the analyzer.
This should then be connected to TD input on the modem, normally Pin 2. If the analyzer
is equipped with a DTE/DCE switch, you may need to change its setting so the signal is
on Pin 2.
Second: Go to the cable connected to the modem/terminal and verify (use a DVM) that
you are getting a -5V to -15V signal on Pin 3 of the cable. This pin should be connected
to Pin 3 of the Teledyne API analyzer.
Third: (for modems) Check that the voltage level on Pin 8 of the analyzer is between +5V
and +15V. This pin should be connected (through the cable) to Pin 4 of the modem.
Now set the baud rate of the analyzer to the speed required by the modem and it should
work. If you are still experiencing problems, a cable adapter may be needed. Please
contact the factory for assistance.
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