Checking A Monitor Tube

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

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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. - Buy Now! Buy a Alligator Clip Set (10 Pc) from now!

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.

Checking The Tube With An Alligator Clip

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.

Color Transistors And Resistors

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.

  1. Avatar
    Wes Benson

    I do not know anyone that has knowledge of Arcade monitors. Watching videos like this is the only way for me to learn this stuff.
    Thanks for the helpful tips you guys rock

  2. Avatar

    Thank you for posting up all of these videos!! I watch them all just to know what to look out for, you guys are great!!


    Again, thank you!

  3. Avatar
    Mark DeRidder

    This is a very cool technique and was working very well for me until I touched the wrong silver dot on the back of that board and after a small electric pop the monitor turned off and won’t turn back on again. Did I blow a fuse or trip a reset? Any quick fix to bring the power back to the tube or is it shot now? Everything else is still working but no picture at all now. Need some help here.


  4. Avatar
    Jonathan Leung


    I sent your question to our resident monitor repair guy Michael and here’s what he said:

    Most likely he touched the G2 wire (focus) and probably shorted out the HV section. It may have just blew a fuse depending on the chassis. Tell him to check the main fuse, and if that is blown check the HOT. If the HOT checks bad, just replace it and the fuse. If the HOT is good then he may get by with just a new fuse. If the fuse checks good, then the HOT could still be bad with a small ohm resister open off the collector of the transistor. In that case, the resistor and the HOT will need to be replaced. That may be hard for him, depending on his experience because he will have to know the value of the resistor and the watt rating. Hope this helps.

    Thank you for your question and good luck with your repair.

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