Oki ML390 Service Manual page 200

4.9.04 Serial Interface Loopback Test
NOTE:
Attach a serial loopback test connector to the printers serial port to run this test.
General Information
The Serial Interface Loopback Test checks the operation of the serial interface board.
Procedure
· Verify that the ribbon and paper are installed.
· Power ON the printer.
· Press MODE. The SEL light will go out and the MENU lamp will light.
When the MENU lamp is lit, the functions printed BELOW the operator panel switches are activated.
· Press GROUP until you access the desired group (Serial Interface). Each time you press GROUP, the
printer will print the current group.
· Press ITEM until you access the desired item (Diagnostic Test).
· Press SET until you access the desired setting (YES).
· Press MODE to record the changes and return to Print Mode. The MENU lamp will go out and the SEL
lamp will light.
· Power OFF the printer.
· Attach the loopback test connector to the printers serial port.
· Verify that continuous feed paper is installed.
· Power ON the printer.
· The message LOOP TEST will print.
· The memory buffer size will print.
· The test checks the memory function of the memory buffer.
OK will print if the memory check passes.
BAD will print if the memory check fails.
· One of the following messages will print next.
I/F Good
If the message I/F GOOD prints, no problems were found.
I/F BAD
If the message I/F BAD prints, a problem was found.
· Hexadecimal characters 20 through 7F are transmitted through the transmit data (TD) line.
Service Guide ML390/391
Chapter 4 Failure & Repair Analysis
Page: 107