A common mistake is not having the daughter card inserted correctly, either hanging over the socket by 1 pin, or in backwards. In this case the screen will be blank and the start LEDS are probably lit.
Another common mistake is for the 6502 CPU to have been inserted incorrectly, either backwards, or possibly with a pin bent that did not insert into the socket properly.
The Battlezone high score save kit will perform a very simple powerup selftest of the HS daughter card when the game is placed in selftest mode. Two additional lines of text are displayed during selftest that relate to the HS kit.
The first line either displays "ROM FAIL" indicating that the code eprom on the daughter card is defective, or it displays the rom revision (eg. "REV 00A") if the code eprom is good.
The 2nd section displays information about the HS save chip on the daughter card. It displays "HS FAIL" if that chip is defective, or it displays "ERASED" if all the scores have been erased, or it displays nothing if the chip is functioning properly.
Should you see the text "HS FAIL" during selftest it most likely that means that one of the socketed chips on the daughter card is probably lose. Check to make sure the 8-pin dip (the smallest chip) on the HS daughter card is fully inserted into its socket.
Battlezone high score failure
Battlezone rom failure