Embedded Thermal Printer not functioning

I purchased 4 Embedded Thermal Printers (DFR0503-EN) and none of them work.  I'm trying to print from an Arduino using the serial input.  

I've tried:

- Printing to another thermal printer (a larger one I purchase a few years ago).  That worked fine.

- Printing at both 9600 and 19200 baud (neither worked)

- Trying many different sketches.  The simplest is copied below.

- Powering the printer at 5v and 7.5v, from separate power source

I also found that the cables were reversed - the yellow and green wires (which are usually the TX and RX leads) are not the right leads into the printer.  I made sure I was sending signals to the correct inputs on the printer.

I tried a few of the code snippets you listed in the product wiki.  None worked.

Nothing has worked.  Can you give me any help?

Thanks,

Dave

=====================================

CODE I TRIED:

#include <SoftwareSerial.h>
SoftwareSerial mySerial(2, 3); // RX, TX

void setup()
{
 mySerial.begin(9600);
 //mySerial.begin(19200);
}
void loop() 
{
 mySerial.println("Executing now");
 mySerial.println();
 mySerial.println();
 mySerial.println("DFROBOT");
 mySerial.println("Test 1");
 mySerial.println("Test 2");
 mySerial.println();
 mySerial.println();
 mySerial.println("Done");
 delay(5000);
}