I'm trying to do maintenance on my stereo system and I know that capacitors will hold an electrical charge, but is there anything else that could shock me? I'm not sure this is the right place to ask this, sorry if its wrong.
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1\$\begingroup\$ Capacitors are the repository of charge. Inductors can also store energy, but as soon as the supporting currents are removed they collapse their fields and the energy is immediately removed (or distributed to capacitors.) So if the unit is unplugged long enough, the only remaining energy sources with any storage duration will be capacitors. Any voltages above about \$50\:\textrm{V}\$ are considered to be potentially dangerous. So if your stereo system is below about \$50\:\textrm{W}\$ per channel (about \$\pm 30\:\textrm{V}\$ rails), you are probably relatively safe, regardless. \$\endgroup\$– jonkCommented Jan 8, 2017 at 20:55
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3\$\begingroup\$ I've seen some pretty awful designs (especially by noobs posting questions) that have shocked me. \$\endgroup\$– Andy akaCommented Jan 8, 2017 at 20:56
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\$\begingroup\$ Also, to gain UL approvals, the male contacts at the AC plug end cannot expose you to significant shock hazards. When you unplug a UL approved device, you should be able to touch the removed metal blades at the plug end without shock risks. \$\endgroup\$– jonkCommented Jan 8, 2017 at 20:59
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\$\begingroup\$ @jonk <34 V after one second. No real requirements on internal capacitors during service but I've seen one minute as an industry standard. Measure first though! \$\endgroup\$– winnyCommented Jan 8, 2017 at 22:48
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\$\begingroup\$ Jonk's suggestions are appropriate for solid-state amplifiers. If it contains vacuum tubes (valves), then capacitor voltages will be considerably higher than 50V, even for a lower-power amplifier. \$\endgroup\$– glen_geekCommented Jan 9, 2017 at 2:02
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2 Answers
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If the electronic device is an old box type television, then you wanna watch out for the tube behind it as it produces a huge amount of current even after it's turned off. I had an experience where it hit my head with my brother's!
And then charged capacitors can do the same but I'm not sure if any can be as bad as that TV experience.
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As long as the stereo is unplugged from the AC mains, it is mostly the capacitors that you have to worry about.
There are a few less common sources of unexpected voltage that are easy to disconnect:
An antenna going to the roof could get hit by lightning.
The Cable TV connection sometimes has an AC or DC voltage on either the shield or the center conductor, much higher than seems reasonable. The shield is supposed to be properly grounded at the entry to the building, but sometimes it is not. It can be a big surprise! The center conductor sometimes has DC on it for power.
