MAMEWorld Forums - EmuChat - Re: Star Trek arcade by Sega (Video)

> I meant compared to a conventional raster display. In my admittedly very limited
> understanding, a vector monitor draws only dots and the game, or vector generator or
> whatever, has direct control of the beam or the guns at all times.

It's still purely a CRT characteristic. The difference between a vector monitor and a raster monitor is all in the way the beam deflection is controlled. In a raster display you have ramp generators causing it to scan in a fixed pattern. You can still get that glow effect by turning up the drive really high, but you generally wouldn't as it messes up your picture when bright stuff bleeds (or "glows") into the surrounding areas.

> I remember reading about a "spotkiller" circuit which does something to the beam so
> that it doesn't burn a hole in the phosphor? I used to own an Asteroids upright and
> you could see it in action as you turned the game off and the beam would sort of
> zinnggg onto the center of the screen, concentrated and bright like the shots and
> then disappear. I always imagined that that was the "spotkiller".

Yes, keeping the beam at a single point for too long will damage the phosphor. You can do this on a raster monitor by disconnecting the horizontal or vertical drive (causing the beam to scan along a single vertical or horizontal line) or both (causing the beam to stay on a single spot in the middle of the monitor). Or the drive circuitry could fail and this could happen without you disconnecting anything.

In a vector monitor, you don't have ramp generators continuously producing a scanning pattern, as you want to trace out arbitrary patterns. In case of a software failure, it could keep the beam switched on and held at a single point or tracing a small area repeatedly. Note that with a vector display this would only require a software failure, not a hardware failure or disconnecting drive electronics.

The spotkiller is supposed to detect cases when the beam is being held in a pattern likely to cause phosphor damage and switch it off in such cases, to help protect your investment.

But at the end of the day, CRTs are pretty much the same whether they're being used for vector or raster display. The ones that are actually different are the radar and oscilloscope displays that use electrostatic rather than electromagnetic beam deflection, and the storage CRTs in some vector terminals with a grid that allows them to "hold on" previously drawn vectors without needing to refresh them.