Re: Ampliphone HV-other options?!

On Sun, 13 Jun 1999 19:46:15 -0600, "Keith, Brendan" <Brendan.Keith@wilcom.com>
wrote:

>That just made me think of a trivially easy Cine monitor tester
>for when your game board is down.
>
>Since the inputs typically float high and move the beam to the corner
>and result in all the usual mayhem, a small adapter that grounds the
>inputs would center the beam.

Actually it's not the inputs floating that causes this. The inputs are digital,
and most likely either pull themselves high or low, though it is possible they
might oscillated between the two, but either way the beam does not see these
values.

What happening is C101 and C201 (Reference is the RipOff monitor schematic),
start out at zero. And then start to charge one way or the other (through
leakage currents in IC1 most likely, though it could also be leakage currents
through IC102 and IC202). The output trace follows this charge until the beam
is far enough off the screen to trigger the circuit breakers.

One way to stop this would be to turn on IC1 so that the cap follows the DACs.

But this must be done very carefully!! The X/Y amplifiers cannot handle the
full value of these DACs!! If either of these DACs were to come up full
negative or full positive the CRT beam would be slammed to it's maximum value
you'd better hope those breakers are very fast acting!

The way the Cinematronics monitor works is to set the cap to a starting value,
then set the ending value *way* off the screen. The capacitor will start
charging quickly to reach the given goal. This make for a visually straight
line. (The lines drawn on a Cinematronics monitor are not really straight, but
follow the curve of a charging capacitor, you only see the "straightest" part of
the curve however.) Once the length of the desired line is reached, the analog
switch is quickly turned off (along with the beam) and the charging stops, well
before reaching the value that was set into the DAC, were that value to be
reached, the circuits breakers would blow, along with other possible damages.

A simple adapter could be made that would hold the DACs to zero, and turn on the
analog switches. This would keep the monitor in a safe state when powered on.

You could probably even add pull up resistors to the monitor that would put it
into a safe state on power up. Cinematronics, I'm sure, just didn't want to
spend the money on components that are superfluous during game play.

> Then if a simple circuit could toggle the
>2nd MSB on each DAC, 90 degrees out of phase, it would draw a
>square test pattern for monitor troubleshooting. A lower order bit would
>yield a smaller square but I figured this would be a good size.
>I guess a binary counter in Gray mode would work: 00,01,11,10.
>A regular counter, going 00,01,10,11 would give a figure 8 pattern like:
> ----
> \/
> /\
> ----

You have to be careful here as well, the monitor was not made to be driven in
this mode.

In the later models a current limiting resistor was placed between the analog
switch and the position capacitor. Without this resistor some high current
spikes can pass through the analog switch, destroying it.

Without this resistor (like earlier models of the monitor) if the above pattern
were to be made too large, this pattern would absolutely destroy the analog
switch. Unless you were to turn on the "line draw" side of the switch instead
of the "line set" side, in which case you would get a "really roundy" rendition
of the above, as the capacitor tried to follow the inputs through a 10k
resistor.

>That might actually be better for setting the center controls.

The centering controls on the Cinematronics monitor are there to calibrate the
analog circuits with the very critical CPU line draw timings. In order for you
to generate a calibration pattern, you'd have to match the timings of the CPU
line generator, pretty much down to the clock cycles. This means controlling
the "Line set" and "Line draw" inputs precisely.

I've always thought you could do something like this by controlling the
Cinematronics monitor directly with an AVR, or something. Of course at that
point you'd have the makings of a new X/Y vector generator. Just add color to
taste! (Or use the Boxing Bugs color board).

-Zonn
Received on Tue Jun 15 00:08:05 1999