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It has been suggested that I have not emphasized the dangers of servicing electronics enough in these forums. There are, obviously, many ways in which working with electronics can be hazardous, so this thread will be dedicated to discussing these dangers and proper ways to mitigate them.

One excellent place to start and a suggested read for EVERYONE is:

http://www.repairfaq.org/sam/safety.htm
 

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If I may,

One of the biggest dangers of working on electronics whether it be a TV, computer or receiver is that even though you have unplugged the power there are still very dangerous voltages present for even up to 4hrs after the incoming power has been removed.

Capacitors hold a very high voltage that can kill you. Capacitors are like a battery but will discharge all of its charge instantly if you touch the leads. Never assume that the voltage inside the hood is gone even after a short time.
 

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Also be aware that consumer electronics are only meant to be opened by trained personel.
A lot of equipment isn't earthed either, simply relying on "double insulation" to meet local approval ratings.
I recently opened my Pioneer VSX710 and was amazed that the mains terminals & selector switch were not covered in any way. It would be very easy to inadvertantly come in contact with them if you weren't careful.
 

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Discussion Starter #4

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Good links to understand capacitor charging and discharging:

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/capdis.html

http://www.repairfaq.org/sam/captest.htm#ctsdc



Generally, capacitors can be safely discharged using a resistor (to chassis ground or between legs) of between 10 and 100 ohms per volt for the rated voltage of the capacitor. This will avoid damage to the capacitor by discharging too rapidly, as well as prevent dangerous and uncontrolled arcing.
Very good thread and advice. As far as discharging capacitors, it is a very well accepted practice in the custom stereo for auto industry as may have 'open' capacitors in the rage of 1 - 5 Farads (yes, that is correct, HUGE capacitors).

One other note I'd like to mention is that most equipment uses lead based solder (except for a few manufactures that are getting away from using lead). This can be a lot more toxic then one thinks, especially if handling it frequently. Venting of the work space to the outside (or through a system that's made to absorb fumes) should always be used - plus no eating while soldering until hands are washed. Heavy metals build up in the liver and are never release from the body. I've done my share of 'toxic' inhalation from a lot of past soldering (am very careful now).

Thanks for starting this thread! This should be noted in all DIY areas.

Ray
 

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Discussion Starter #6
Very good thread and advice. As far as discharging capacitors, it is a very well accepted practice in the custom stereo for auto industry as may have 'open' capacitors in the rage of 1 - 5 Farads (yes, that is correct, HUGE capacitors).

One other note I'd like to mention is that most equipment uses lead based solder (except for a few manufactures that are getting away from using lead). This can be a lot more toxic then one thinks, especially if handling it frequently. Venting of the work space to the outside (or through a system that's made to absorb fumes) should always be used - plus no eating while soldering until hands are washed. Heavy metals build up in the liver and are never release from the body. I've done my share of 'toxic' inhalation from a lot of past soldering (am very careful now).

Thanks for starting this thread! This should be noted in all DIY areas

Ray
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All new products use lead free solder. IME lead is far less of a hazard than suggested. I have worked with leader solder for 30 years and have been tested several times with negative results. I suggest reasonable care in using lead based solder, but it really is not great hazard. The fumes contain other hazardous substances but not lead.
 

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Icaillo,

I want to thank you so much for sharing a LOT of info in so many threads!!! I'm still reading some of them, very thoughtfully put together with great incite and care! Much appreciated.

Ray
 

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Discussion Starter #10
Actually, a capacitor will discharge no differently than a battery. The rate of discharge depends on the voltage and the load attached to it. Capacitors can often have much higher voltages than batteries, but cannot deliver current for as long a period. With respect to safety, it is always wise to confirm that the larger caps in a device are discharged properly before working on the device.
 

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If one has absolutely no training in electrical / electronics work I would highly discourage poking around inside. However, it is not difficult to get some basic instruction so that you can poke around with some level of safety. Take a basic electronics class locally or work through a lab kit at home. The organized class is preferred because you will be introduced to the equipment and you will have an instructor to guide you.

Even seasoned professionals make mistakes - I personally have had many but for example I melted a large screwdriver on 440 volts that was supposed to be turned off (The shop owner turned it off and I didn't check). I took 25 kv on the chin from a color TV transformer. Etc. There are lots of stories out there.

But there are definitely some basics that you should know before you go for it. As an example (and not for opinion on the issue) it would be foolish to own a gun without taking a firearms safety program or having been taught by a pro somewhere. Electricity can also kill.
 

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Capacitors are used to either smooth out DC voltage, block AC voltage, pass AC voltage, keep noise off the supply voltage, or combine with other components to create a tuned circuit that will block or pass certain frequencies like in a crossover. The most common caps used in standard electronics are so small that even if discharged it would feel like static electricity because they simply don't hold much energy. Even the basic assortment of electrolytic caps.

But a standard power supply in a device can store up a good shock. And TV's have serious high voltage supplies. These all need discharged correctly.

The large caps used in car audio are a different story. Any capacitor bigger than your thumb probably is going to hurt you. That doesn't mean you shouldn't use caution on any size electrolytic capacitor (these are the ones that look like tin cans). The big ones are truly mini batteries and that is what they are used for. In circuit design 1 farad is about a thousand times bigger than anything ever needed. In fact I don't remember even seeing one that size until "recently". They store a lot of power.

Maybe someone could list the power storage of the different sizes of electrolytic capacitors in a table of some sort for the curious. Start at 10 mf and go up to the big boys. Just an idea.
 

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Discussion Starter #14
Capacitors don't store power, they store charge, and capacitance is the meaningful unit. As you stated, 1 farad is much larger than most consumer electronics require and those are mostly used in car audio or industrial applications. Even a much smaller cap can be dangerous, however, and supplies using thousands of microfarads are common.

The bottom line for safety is to determine if there is voltage on a cap when servicing a unit. If there is, discharge it through a resistor until there is not. Assume that there is no safe level of charge.
 
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