|Buy a new one. Probably cheapest, fastest, and easiest way. |
To fix the one you have, you'll have to replace the PROM chip with a preprogrammed one, or remove and reprogram it with an EEPROM burner.
Take it apart and get the Chip number from the PROM. Get the spec sheets for the PROM and maybe there is a test circuit listed that you can build to "test program" it with.
Maybe someone knows how they do it at the factory.