OKIDATA ML590 Service Manual page 248

4.8.04 Serial Interface Loopback Test
NOTE:
In order to run this test, the serial interface board must be installed with a serial loopback test
connector attached to it.
To perform the serial interface loopback test, follow these steps.
Place the printer in the Serial Diagnostic mode.
Set the Diagnostic Test menu item to YES.
Power off the printer.
Attach the loopback connector to the serial port.
Install continuous feed paper.
Power on the printer.
The message LOOP TEST will be printed.
The size of the Message Buffer will be printed.
Three different messages may be printed next.
If the message OK is printed next, the message buffer has been tested and no problems
were found.
If the message BAD is printed next, there is a problem with the message buffer.
If the message IF BAD is printed, the signal logic was tested and a problem was found.
Hexadecimal characters 20 through 7F are transmitted through the transmit data line.
The receive data line receives the characters.
The message buffer then stores the characters.
The data is then printed.
The test will run until the printer is powered off or the
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Service Guide ML590/ML591
Chapter 4 Failure & Repair Analysis
SELECT
switch is pressed.
Page: 173