Response from Jonathan: Dan,

It’s not uncommon to have some small black spots on your CRT picture but this is definitely the largest one we’ve seen. It’s almost like there’s something on the inside of the tube that’s causing this spot to occur. You could try removing the yoke and repositioning it but we don’t know if that’s really going to solve the issue.

It might be time just to replace the tube altogether. In order to accomplish this, you just need to locate a replacement tube (from a TV, computer monitor, etc.) that has the same yoke readings, neck size and socket pinouts. If the tubes are a match, you should just be able to swap them and leave the original chassis in the game. There’s some great information about how to get the yoke readings (measured in ohms) off your tube at https://web.archive.org/web/20080705201439/http://www.8liners.com/datatech/monitor.html. There is also a nice list of donor TVs for arcade pictures tubes here: http://junknet.net/donor-tvs.

I’ve also forwarded your email to a couple of our monitor repair specialists to get their thoughts on your issue. I’ll let you know what they say once I hear back from them.

Hope that helps. Thank you for your question and good luck with your repair.