# What can shock you in an unplugged electronic device?

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.

• 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. – jonk Jan 8 '17 at 20:55
• I've seen some pretty awful designs (especially by noobs posting questions) that have shocked me. – Andy aka Jan 8 '17 at 20:56
• 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. – jonk Jan 8 '17 at 20:59
• @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! – winny Jan 8 '17 at 22:48
• 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. – glen_geek Jan 9 '17 at 2:02