What is a CRT monitor?
Before LCD flat panels replaced them during the 2000s, nearly all computer monitors and TVs used cathode-ray tubes. An electron gun at the narrow back of a large glass vacuum tube fires beams that magnetic deflection coils (the yoke) sweep across phosphor dots on the inside of the screen, which glow to form the image. That design explains why CRTs are deep and heavy and why they need very high voltage to accelerate the electrons. You will rarely deploy one today, but they still turn up in storage rooms, labs, older industrial equipment and recycling piles, and on the exam they are a safety and disposal topic.
Hazards
- Stored high voltage: the tube and its high-voltage circuits can hold a dangerous charge long after the monitor is unplugged. The tube itself behaves like a capacitor. Discharging it safely takes special tools and training.
- Implosion: the tube is under vacuum. Cracking the glass or snapping the thin neck at the back can make it implode and throw glass.
- Lead and other toxic materials: CRT glass contains lead to block the X-rays produced inside the tube, and the coatings and circuit boards contain other heavy metals. That is why CRTs are treated as hazardous waste in many places.
- Weight: large CRTs are very heavy. Lift with your legs, keep the load close and get a second person for big units.
Safe handling rules
- Never open a CRT monitor or try to repair its internals. Like a power supply, it is replaced, not repaired, by a desktop technician.
- Do not wear an ESD wrist strap near exposed high-voltage parts such as an open CRT or power supply. A wrist strap gives static a path to ground, and near high voltage you do not want your body connected to anything.
- Never lift or carry the monitor by the narrow rear of the tube.
Disposal
CRTs do not go in the regular trash. Many U.S. states and other jurisdictions restrict or ban sending them to landfills and require recycling through an approved e-waste recycler or a take-back program. Follow local regulations and your organization's disposal policy, check the manufacturer's documentation or safety data sheet (SDS) where one exists, and keep the recycler's paperwork as proof of proper disposal.
CRT vs LCD and LED displays
| Feature | CRT | LCD/LED |
|---|---|---|
| Size and weight | Deep and heavy | Thin and light |
| Internal voltage | Very high, stored after power off | Low, apart from older CCFL backlight inverters |
| Hazardous materials | Leaded glass, heavy metals | Circuit boards; older CCFL backlights contain mercury |
| Typical quirks | Burn-in from static images, color patches from magnetism | Dead pixels, backlight failure |
Many CRT monitors had a degauss button that removes stray magnetism causing color patches. That is a different use of the word from degaussing a hard drive to destroy its data.
CRT monitor on the CompTIA A+ exam
Core 2 (220-1202) objective 4.5 covers environmental concerns, including proper disposal of devices and assets, and CRTs are a classic example. If a question asks how to get rid of an old CRT, think local regulations and an approved e-waste recycler, never the trash. If it asks whether a technician should open a CRT to fix it, the answer is no, because high voltage remains even when unplugged. If a question pairs a CRT with an ESD strap, remember that you do not wear a wrist strap around high-voltage components.