Checking A Monitor Tube

Even though most monitor issues can be traced back to the chassis, there may be some instances where the tube is at fault. Missing colors, color smearing or screen blurring are just some of the symptoms that might indicate a bad monitor tube. In this post, we will discuss how check a monitor tube and troubleshoot other monitor color issues.

Checking A Monitor Tube

First off, let’s discuss some of the different symptoms you might be experiencing if you have a bad tube. The most common symptoms of a bad tube are missing colors, color smearing or streaking, convergence issues and/or screen blurring (especially in the corners). Keep in mind that in some of these cases you might be able to do some minor tweaks to fix the issues. If your screen is out of convergence, you might take a look at our post on Adjusting The Convergence Rings before suspecting your tube. The same goes for color issues as Adjusting An Arcade Monitor might help fix them without the need to test the tube. Since the tube is usually not the problem, make sure that you’ve exhausted some of your other resources before putting the blame on it.

Once you have exhausted some of the more common chassis repairs, we can move on to testing the tube. Before we begin the process, you will need a wire with alligator clips on each end. You can either make one your self (which is a similar process to what we talk about in our post on Safely Discharging An Arcade Monitor) or you can purchase one from your local electronics store. It is also a good idea to have a mirror positioned so that you can see the screen or a friend that can tell you what’s going on while you are doing this process.

Now that we have our wire with alligator clips on the ends, we can test our tube. Take the back door off of your game so that you can gain access to the back of the monitor. Clip one alligator clip to a ground on your monitor (such as the frame). Look at the back of your monitor’s neck board and identify which of the circular points control the colors. Most of the times these are labeled to make it easy for you. When you have identified the color pins, quickly touch the non-clipped end of wire to the pins and see what happens on the screen. Be careful not to hold the end of the wire on the pins for too long. When you do this, you should get a bright screen just featuring the color pin that you touched and some retrace lines. If this does not happen then it could mean that the tube is bad and needs to be replaced.

Let’s say that your tube is good but you are still having some missing color issues. It could be that some of the parts on the neck board are malfunctioning. There should be a transistor and a resistor located on your neck board that drive each of the primary colors. You can check the transistors by removing them from the neck board, setting your multimeter on continuity (or diode) test and checking the continuity between the pins. If you do not get continuity then you probably need to replace your transistor.

Resistors can also be tested with a multimeter but the process is a bit different. Instead of using the continuity (or diode) test, you will need to set your multimeter on Ohms (or Ω). When you put your probes on the leads you should get a reading on your multimeter. If the resistor is good then this reading will be pretty close to the value indicated by the color bands. The Resistor Reader page on Bob Roberts site can help you identify this value. There are also charts that you can buy that will tell you the values of each color band as well.

While many people like to suspect the tube whenever they have monitor issues, this is often not the case. Being able to identify and test a bad tube will save you a lot of time when troubleshooting monitor problems. Please leave any questions or suggestions you have in the comments section below.