Last time I posted, I mentioned that I installed a new cap kit, new flyback, and new HOT on the arcade monitor. However, it was still giving me a green image. Here’s a video of what it looks like:

After some investigations online, I’ve come to the conclusion that it’s a heater-cathode short. What is that exactly?

Every CRT monitor has three electron guns, one for each of the three color components, red, green, and blue. These electron guns fire electrons from the back of the set to the screen, lighting up phosphor, which glows either of the three colors. The electron guns are located inside a vacuum tube and are aided by a heating element. The heating element heats up something called a cathode, where the electrons originate.

The problem is this: if debris collects on the cathode and comes in contact with the heating element you get a “short” in the circuit, which causes the electrons to always fire, even when they shouldn’t be. For instance, if the green gun has a short, instead of firing only when there are green elements in the pixel, it will always fire. I suspect that’s what’s happening with my screen.

To fix it, I’ve read that you can try plugging a CRT rejuvenator device into the back of the set. What this thing will do is send higher than normal levels of voltage through the electron guns, hopefully burning off the collected debris found in the short. After you burn off the debris, no more short.

A Gallery of Heater-Cathode Shorts

What I found interesting online is that there are very few posts with pictures of this heater-cathode short phenomenon, so I decided I should post some links below in case someone googles this info in the future.

First off, this guy encountered it with his NARC machine and got a green screen very similar to mine above.

Someone else has a bad gun on their vertical setup.

The red gun can also be shorted, as seen by this guy’s Golden Tee machine.More red screen madness on this Mortal Kombat machine.

Yet another red gun shorted.

It May Not Be Heater-Cathode Short

Sometimes you may have a problem in your neck board or the monitor chassis and it may not be a heater-cathode short. To check for this, the general advice I’ve seen is to try check your neck board. The neck board has similar circuits for each of the three color components. If you have a problem, it may be a bad transistor. To test this theory, simply swap transistors between two colors. For instance, if you see too much green on the screen, try swapping the green transistor with the red one and see if the problem becomes too much red on the screen. If it is, then most likely you have a bad transistor.