Oki ML390 Service Manual page 201

· The receive data (RD) line receives the characters.
· The message buffer stores the characters.
· The data prints.
· The test runs until the SELECT switch is pressed or the printer is powered OFF.
· To restore the printer to normal operation, power OFF the printer.
· Press and hold the MODE switch while powering ON the printer. The printer will be in Menu Mode.
· 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 (NO).
· Press MODE to record the changes and return to Print Mode. The MENU lamp will go out and the SEL
lamp will light.
Serial Loopback Plug Diagram
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