WG6100 w/Tempest Showing a Multicolored spot in Center of Screen

So I was helping a newly minted arcade game owner when his first purchase, which is his favorite arcade game: Tempest.  Shortly after getting it the X-Size pot fell apart and the game ended up only showing a Multicolored spot (larger than a just a “dot”) which changed depending on what the game was doing.  We soldered in a larger replacement (dangling from some wires) but while this did change the display a little when the pot was articulated, it did not fix the problem.

He had joined a FB arcade repair group and asked for help there and ended up with ideas ranging from his brightness being too high (it was not – I think the person that responded thought the game was drawing normally but with retrace lines and a white dot in the middle, kind of like how it looks when you’re drawing on an oscilloscope with no Z input), voltages too low (they were not), and one even going down the path of impending AR-II failure(!) and going on about replacing leaky sense resistors and the bottlecap transistor.  Oy vey!

This did not feel like a board or problem even though the mathbox chips were getting hotter than I would like.  I scoped the X-Out and Y-Out test points and the game was drawing normally on the scope.  No scaling problems, nothing out of place – everything looked solid.  Double checked on the monitor connector, and saw the same thing.  While I was up close to the monitor, I noticed that I was not hearing any deflection chatter.  Took a closer look at the monitor board/chassis and realized that the two inner deflection fuses (F600 and F700) were blown.

I would like to take a moment here to describe what just happened.  I call it “failure of the duh reflex.” So… uh… Duh!

Replaced the fuses and the game came mostly up.  It was drawing correctly but was having intermittent collapse in the quadrants.  One of the fuses was glowing orange(!) but did not blow.  Adjusted the size and centering pots and got a stable display.

My theory is that the pot breaking off stressed things out to the point where the fuses went.  The monitor is still a bit finicky, but it is working for now.  (What the monitor did next is covered in the next post.)