LOC have a couple of these Seiko DPU-3445 printers. They usually work pretty well, but typically, one of them stopped working just at the wrong time.
The printer would feed and print out the printer settings sheet (with the printer off, hold down both keys and release the power one first). It just wouldn’t print out results.
The settings sheet showed Data Input as IrDA and the Data Input mode as Auto Select.
These needed changing to:
DIP Switch 1
Data Input: Serial
Baud rate: 4800bps
Bit length: 8 bit
Stop Bit: 1 bit
Data Control: Busy
DIP Switch 2
Data Input Mode : Serial
The way to do this is a little complex, but the manual is available here.
DIP Switch 1 should show 11001010
DIP Switch 2 should show 11111101
No need to change DIP Switch 3.