RE: Asteroids problems...while we're on the subject

> << You might check the voltage outputs and/or current draw on the
> Z-axis
> (try turning the brightness down too). Maybe the extra current to
> draw
> the "bright" dot is causing a little brown-out on the deflection
> power
> supply rails?
> >>
>
> I tried messing with brightness, no luck. Approximately where should
> my Z-axis
> current draw be? I get no problems with the same monitor drawing shots
> when I
> use my working Asteroids Deluxe board with the same monitor, so I'm
> sure the
> problem is not monitor related.
>
I must confess I have no idea what the current "should" be. I'd say to
compare it with the board that works right just to see if something's
way out of whack? I'd start measuring at the game PCB-- check the
output voltage and see if maybe the gun on the monitor is being
overdriven.

I guess it's possible that the transistors in the brightness control
could be freaking out or getting noise too. Asteroids has this little
4-resistor DAC made with about three transistors (two 3906's and one
3904?) that controls brightness. Maybe check the transistors and/or
resistors?

If you have a scope I'd still look at the Z output and see if you can
see anything suspicious there (particularly high voltages). If the
problem is on the game board (I agree that it probably is) you should
theoretically see the "glitches" on the scope too.

You could also just try to easter-egg your way to a solution and try to
clamp things down a bit-- put some tiny (like 10 to 200pF) caps from the
X and Y outputs in series. Sometimes putting them to ground helps.
Maybe put an inductor in series and just see if you can quash the noise
regardless of the source...

-Clay
Received on Thu Jan 14 21:43:47 1999