Brother HL 1240 - B/W Laser Printer Service Manual page 293

Error Message
SERIAL INTERFACE
OVERRUN ERROR
(HL-1250 Only)
SERIAL INTERFACE INPUT
BUFFER OVERFLOW
(HL-1250 Only)
Action
Press the control panel button to resume printing.
If the error occurs again, the interface's hardware may be
damaged. Please consult your dealer.
Press the control panel button to resume printing.
Check the communication parameter settings such as the
handshake protocols on both your computer and printer.
If the error occurs again, the interface hardware may be
damaged, consult your dealer.
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CHAPTER 4 TROUBLESHOOTING