It was discovered that a few Coleco Intellivision games did not work on the Intellivision II. Mattel secretly changed the Intellivision's internal ROM program (Exec) in an attempt to lock out 3rd party titles. A few of Coleco's early games were affected but the 3rd party developers quickly figured out how to get around it. Mattel's own "Electric Company Word Fun", however, will not run on the Intellivision II due to this change. In an unrelated issue but also due to Exec changes, Super Pro Football experiences a minor glitch where the quarterback does not appear until after the ball is hiked. There were also some minor changes to the sound chip (AY-3-8914A/AY-3-8916) affecting sound effects in some games. Programmers at Mattel discovered the audio differences and avoided the problem in future games.