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Degauss circuit help


DevoDave

Question

Hi,

 

Got a Neo-Geo in an LAI cabinet. There is a degauss button (and connector) on the 240V switchpanel/breakout.

 

The existing wiring for the degauss circuit has the degauss pulse from the monitor chassis going off to the degauss coil, but the switch is wired in series with the pulse. (See my uber great diagram.)

 

Now, my understanding is that the chassis should pulse the degauss coil each time it is turned on. With the cabinet wired like it is, I cannot see how this could happen.

 

Also, when the button is pressed, as the degauss circuit has already been powered up for a while, will anything actually happen?

 

So I really need to know if this circuit is correct or is there a better way to wire up this baby.

degauss.gif

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If it uses a 2 pin PTC on the board then this would be right. The switch will initiate the degauss (press and hold) but the PTC stops it from going on for too long.

 

The PTC will only change state when the coil draws current so will work even if the chassis has been powered up for any length of time.

 

It also means you can fire the degauss multiple times (with a cool down period each time) without powering the chassis down.

 

The PTC also means that a stuck switch won't result in a meltdown of the coil.

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As most automatic deguassing ie pretty much a waste of time, this manual approach probably works better.

One assumes that you have actually traced it out correctly, and it is not looped on the chassis itself, As most ccts use a ptc thermistor to control the switching of degaussing.

I have come across dozens of chassis where the degaussing has been disconnected.

Sorry David looks like we reply at the same time.

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Sorry, I should have mentioned that. Yes, Hewitson is correct with the PTC & NTC info.

 

Interestingly it applies to any electrical parameter, not just resistance.

 

With capacitors (usually in the pf range), you even get NPO types.

This means that the capacitance neither increases or decreases with temperature.

The make the capacitor with N & P coefficient parts that cancel each other out!

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My chassis has 2 seperate deguass coils that both sit at the small sides of the screen (vert screen so top and bottom). The thing is they do nothing at all. I still have 2 areas needing deguass...the bottom right, and top left of screen. I took the coils off and it made no difference, so going to buy a wand soon. I also ran a magnet about 5cms above the effect parts of the screen and whilst I held it there it was perfect.
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