Defender Image Issue

My Williams Defender system is currently displaying it’s video image as follows:

Jonathan at Arcade Repair Tips seems to think it is a board issue and suggested reading an article on MikesArcade website on general issues with Williams systems. He also suggested reaching out to Ken/YellowDog on the KLOV Forums. I sent Ken a private message to get his thoughts on the matter.

Didn’t hear back from YellowDog for a day, so I decided to post my issue to the Arcade Museum forums.

The members over at the Arcade Museum forums were very helpful in trying to troubleshoot the issue. The most promising diagnosis was proffered by seanriddle who even tested out his hypothesis on the MAME version of the Defender game. He suggested the problem most likely lies with the 74165 chip at board position 1O, which is responsible for the video out display for player 1:

He suggested testing out the hypothesis by enabling the cocktail mode of the game, which “flips” the screen for player 2. The flip activates the second set of 74165 chips to the right of the bad one and if the hypothesis is correct (and the second set of chips are in sound shape), the lines should disappear. Now I just need to figure out how to set the cocktail mode. According to seanriddle, this involves moving 2 jumpers on the control panel board. Off to check that out…