CRT monitor safety
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⚠ Safety guide. This page covers hazards that can cause serious injury or death. Read it fully before you start, and if you're unsure, stop and ask someone experienced.
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! Topic
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! Tools needed
| Safety glasses
Insulated discharge tool
Alligator clip lead
Isolation transformer
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CRT (tube) monitors are the most dangerous part of an arcade cabinet. Some pinball machines also have small CRTs or other high-voltage displays.
Why CRTs are dangerous
- Very high voltage. The picture tube runs at roughly 20,000–30,000 volts.
- It stays charged after unplugging. The tube acts like a capacitor and can hold a charge for days or longer.
- It can recharge. A tube that has been discharged can build up a charge again on its own over time.
- The glass can implode. The tube is under vacuum. If the neck or face breaks, glass can fly.
Before you touch the monitor
- Unplug the machine and wait several minutes. See Before you open a machine.
- Wear safety glasses.
- Never lift or hold the tube by its thin neck. Lift by the frame or mounting ears.
- Never work on a powered monitor without an isolation transformer.
Discharging the tube
The anode is the thick red wire that ends in a rubber suction cup on the side or top of the tube. Under that cup is a metal clip carrying the high voltage.
- Use a discharge tool: a long, insulated screwdriver or probe with a wire clipped to its metal shaft.
- Clip the other end of that wire to the tube's ground: the metal braid or wire running around the back of the tube, or the metal frame the tube is bolted to. Don't clip to a circuit board.
- Hold the tool only by its insulated handle, using one hand.
- Slide the tip under the suction cup until it touches the metal clip. You may hear a snap.
- Hold it there for a few seconds, then remove and repeat a couple of times.
- Discharge again any time the monitor has sat for a while.
If you have any doubt about doing this safely, don't. Ask someone experienced or have a monitor technician do it.
Other monitor hazards
- The flyback transformer and the parts near it carry high voltage.
- Large capacitors on the monitor chassis can hold a charge. See Replacing capacitors.
- Never remove the anode cap while the monitor is powered.