The best and cheapest practice in fixing communication failures is to have a stock of serial drivers. These chips are a common cause for failure when there are surges, spikes, and lightning strikes. The only processor board that does not have removable serial drivers is the MilTouch™ processor boards. In addition, all peripheral boards like the I/O, Output, A to D, and D to A boards have a removable serial driver.
Other possibilities for failure could be a change in configuration. This is something to check after replacing a processor board or installing a new EPROM software chip. Baud rate is another communication point that needs to be set properly. This determines the speed we are expecting to send and receive data. When the baud rate of two machines do not match, then there is usually a failure to communicate.
When replacing peripheral boards and processor boards, be sure to set the address on the board exactly as the old board.
What does the serial MTA Connector connect to?