CRT:CRT Safety Warnings/Tips

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CRTs are not a good place for people who are beginners with repairing electronics, as they can be potentially dangerous.

Electrical Safety

Exclamation-triangle-fill.svgSome RF-only sets from the 70s and 80s have a "hot chassis", meaning the entire metal chassis can be at mains potential and shock you. See the "Testing for a Hot Chassis" section below if you suspect that you have a hot chassis.

  • Always check to see if your specific model has a service menu that could be used to make whatever adjustments you are needing to make without opening the set. This menu is often hidden behind a specific button combination.
  • The largest risk of injury is the large amount of charge that a CRT uses. Even when unplugged, the capacitors in the CRT can give off a nasty shock. It is a dangerous amount of charge and could potentially be fatal depending on how the shock goes through your body and if your heart is weak. Even if you are healthy, a large shock can knock you backwards and cause fall injuries. While some professional CRTs naturally drain off their accumulated charge, you should never rely on that feature to be operational. If possible, work on the CRT with the power OFF and discharge the CRT.
  • If the CRT has to be powered on when adjusting it:
    • Observe the "one-hand" rule. Only ever stick one hand into the CRT, and keep the other in your pocket or behind your back. This will ensure that you will not touch two points and have current flow through your arms and through your heart.
    • Remove any rings on your hands that could potentially bridge electrical contacts.
    • If working on a live CRT, use plastic or wooden tools to perform adjustments to avoid the possibility of bridging electrical contacts with a metal tool.
    • Optionally use electric lineman gloves + leather over-gloves.
    • Avoid the areas around the anode cap (underneath the suction cup on the back of the tube) and the flyback transformer. Also any AC power circuits are potentially dangerous.

Testing for a Hot Chassis

As a cost-savings measure before the mass production of switching power supplies, CRT sets were produced without isolating the power rails from mains power. Because of this, the chassis can be at mains voltage level and shock you. Generally, this is limited to RF-only CRT sets from the 70s and 80s. The solution to this is to plug the CRT set into an isolation transformer if you need to work on it while is powered on.

To test for a hot chassis:

  1. Unplug the CRT set and turn the power switch on.
  2. Using a multimeter in diode check mode, check to make sure that all four of the below scenarios show "OL" (i.e. no diode and no continuity). If any detect a diode or short, it is a hot chassis.
    1. Red probe on prong #1 of power plug and black probe on chassis.
    2. Red probe on prong #2 of power plug and black probe on chassis.
    3. Black probe on prong #1 of power plug and red probe on chassis.
    4. Black probe on prong #2 of power plug and red probe on chassis.

Discharging Instructions

  1. Unplug and press power button to turn it to the ON position. Recommended to let sit for a day, then discharge.
  2. Use one of the two following methods:

Lifting Safety

  • Clear the path from start to finish before picking it up. Open doors, make sure no pets can be in the way.
  • Multiple people if possible.
  • Use a dolly or cart if available.
  • Lift with your legs, not your back.
  • Use non-slip gloves to lift if possible. This will reduce the plastic edges digging into your hand and give you a better grip.

Weather Shock Safety

  • If the CRT set has been out in very cold temperatures, allow it a couple days to warm up inside before powering on. CRTs generate a good amount of heat and coupling that with very cold glass could potentially cause an area of the glass to expand quicker than the rest and break the tube.

Dirty Internals Warning

  • If it's been exposed to rain and dirt outside, residue can cause bridging between exposed pins and kill the set.
  • Live near a coast you may have salt build-up that should be cleaned out.
  • Dust blankets components and causes them to heat up and fail faster.
  • See CRT:CRT Cleaning Guide page for tips to clean it out.

Platform Construction

  • Always check the weight rating of the platform that you put your CRT set on. Ikea Kallax shelves are a popular choice for displaying multiple game consoles with CRT TV(s) on top, but their weight rating is for downward force and doesn't take into account shear force if something bumps into the side. It's recommended to have back-planes attached to the back or reinforce individual cubbies with metal L brackets.