CRT-style televisions employed capacitors that retained high voltages (in the kilivolt range) for a long time after the TV was turned off, presenting a danger to DIY electricians who poked around inside the cabinet without realizing what they were getting into.
What sort of operating voltages are present inside a late-model plasma or LCD screen? LCD calculators run on just a couple of volts, so is the same true of an LCD television display? What about the backlights? LED’s are becoming more common, but cold-cathode lighting apparently requires an HV power supply. Do these typically retain high voltage after shutdown, or do they not employ capacitors like CRT TV’s? How about plasma displays?
I don’t know about plasma displays, but LCD panels with CCFL backlights can have a couple thousand volts applied to the tubes. I’ve been poked by more than one CCFL inverter. LED-backlit panels don’t have those kinds of voltages present. I don’t know how long a CCFL inverter retains charge after power-down; when I got zapped it was with the panel operating.
Long, long ago, when I studied TV theory and repair, I read an amusing pullout in one of the books. It explained “secondary effects.”
The zap you get from an unplugged TV can be dangerous, even lethal in the cases of old, giant-tube TVs, but that primary effect was usually harmless. Dropping the TV because the zap startles you is a secondary effect (as is whipping your hand away and injuring it on a wall, sharp edge etc.)… but as the book pointed out, explaining that secondary effect to the customer was likely to be the worst of all, so… (long technical explanation about high voltage safety, discharging caps, etc.)
Has anybody ever actually died from being zapped by a CRT (from the shock itself)? I have had the experience several times before, including while it was powered up (just recently, never trust the rubber suction cup to insulate the HV contact) and while it was fairy shocking, it wasn’t THAT bad (not death, but feeling in any way that it could be, or stunning, making me fall down, etc). The energy storage is too low, based on measured capacitance and voltage (Wikipedia says 5 joules is dangerous, CRTs store less than a tenth of that, probably even for giant 40 inch ones), as is the current capability from the flyback transformer. The power supply in tube TVs would be considerably more dangerous (several hundred volts at a few hundred mA).
As for LCD and plasma displays, LCDs, as mentioned, have a HV inverter generating 1-3 kV if they have a CCFL backlight, but no charge is present when powered off, aside from maybe some residual voltage on the small (10-30 pF) capacitors used to couple the output to the CCFLs (the output is AC though), which store too little energy to really feel. Plasma displays require several hundred volts and can definitely give a good shock (or worse, with hundreds of watts).
Of course, all of these are powered from the AC power line, which is far, far more dangerous than any voltages generated by the circuitry because of the current capability (plus a lot of stuff will shut down if an overload occurs, as when you touch something). This is especially true if there is active power factor correction (pretty much standard now on anything that uses more than 75 watts, even outside of the EU where it is mandatory) since you’ll have up to 400 volts (on either 120 or 240 v mains) at the output with amps of current capability and a large capacitor (plus if a PFC circuit is overloaded, the output can’t be shut off; it will only drop down to the AC input voltage).
I’d say yes, almost certainly, with the highest chances being an early large-screen (24-25 inch) color TV or one of the last-gen mega-tube sets. I had one hand-me-down color TV from about 1970 that weighed 100 pounds and had the kind of jammed chassis you see in military gear. It had HV caps the size of coffee cans and I’ve no doubt that discharging those across your chest (one hand zapped, one hand grounded) could be lethal.
Are you sure those were for the CRT high voltage supply? I have found a few TVs that had a separate capacitor on the CRT HV lead, but these are around 1 1/2-2 inches and up to 1000 pF at 25-30 kV (like this one). The tube TVs I have found never had any capacitors I’d describe as being “coffee can size”, unless you mean these large silver capacitors usually around 1-1 1/2 inches wide and up to 6 inches long, rated at up to a few hundred uF at several hundred volts for filtering the power supply for the tubes, but not the CRT HV supply (actually no more, and even less, than capacitors used in modern equipment; for example, I recently used a 680 uF 400 volt capacitor (also much smaller than those in tube sets) in a 600 watt power supply - now THAT packs quite a punch at 49 joules when charged to 380 volts when running, but it has nothing on this 800 joule monster).
The worst part about handling a tube monitor is not the capacitors on the chassis itself, it is the tube itself which can store a huge charge when it hasn’t been discharged. I have seen a tube on a tiny monitor arc as I pulled the flyback anode away a good few inches while the anode was in my hand, I was GLAD it insulated me from feeling that.
Anyways the answer is surely, 100% yes that someone somewhere had a heart defect and got a jolt and died, or found OUT they had a heart problem when they died by getting zapped working on a monitor somewhere, the question comes up in the arcade collecting community sometimes but no one has a cite, but I’d be more surprised if no one had ever gotten killed from high voltage from monitors than if someone hadn’t, it’s very dangerous and even people who ostensibly know what they’re doing get some good shocks.
The B+ capacitors are only rated for a few hundred volts though; I am referring to the CRT itself, which might be a few hundred to a thousand pF (picofarads, 1,000,000 times smaller than a microfarad) (including an accessory capacitor in some TVs, including those with a voltage multiplier and some flybacks), or a few hundred millijoules of energy (as I said before I have gotten shocked before and while it is certainly nasty it is nothing like “thrown across the room”, passed out, etc (Wikipedia actually says that static electricity shocks can go up to 500 mJ, which is similar; my memory may be distorted by time (I was a little kid then) but I vividly recall having a static spark that must of been 1 1/2-2 inches long jump from me after going down a plastic slide and it felt similar).
That is to say, CRT TVs/monitors don’t actually have more dangerous charges in the capacitors that other line-powered equipment, especially with the move to power supplies with PFC (especially in the U.S., where peak line voltage is around 170 volts but PFC circuits regulate it to 380 or so regardless of line voltage and aren’t really current limited since they are usually boost converters which can’t shut the output down completely), energy storage also increases as voltage squared; a 100 uF, 400 V capacitor can store as much energy as a 400 uF, 200 V capacitor, or a 16 F, 1 V capacitor, and of course higher voltages are more likely to break down the insulation of the skin).