Amatuer radio equipment like TVs, computer monitors, microwave ovens, and other electronic equiptment use voltages at power levels that are potentially lethal. Normally, these devices are safely enclosed to prevent accidental contact. However, when troubleshooting, testing, making adjustments, and during repair procedures, the cabinet will likely be open and/or safety interlocks may be defeated. Home-built or modified equipment, despite all warnings and recommendations to the contrary - could exist in this state for extended periods of time - or indefinitely.

Depending on overall conditions and your general state of health, there is a wide variation of voltage, current, and total energy levels that can kill.

The Swan 117CX power supply has voltages approaching 1kV which could be potentially leathal. In addition, if line connected ie. plugged into a 120 outlet the power supply can be potentially more dangerous than the high voltage due to the greater current available. A few hundred volts can make you just as dead as 1 kV!

The following guidelines are to protect you from potentially deadly electrical shock hazards as well as the equipment from accidental damage.

Note that the danger to you is not only in your body providing a conducting path, particularly through your heart. Any involuntary muscle contractions caused by a shock, while perhaps harmless in themselves, may cause collateral damage. There are likely to be many sharp edges and points inside from various things like stamped sheet metal shields and and the cut ends of component leads on the solder side of printed wiring boards in this type of equipment. In addition, the reflex may result in contact with other electrically live parts and further unfortunately consequences.

The purpose of this set of guidelines is to make you aware of the appropriate precautions. Repair or modification of ham radio equiptment and other consumer and industrial equipment can be both rewarding and economical. Just be sure that it is also safe!

• Don't work alone - in the event of an emergency another person's presence may be essential.

• Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system.

• Wear rubber bottom shoes or sneakers. An insulated floor is better than metal or bare concrete but this may be outside of your control. A rubber mat should be an acceptable substitute but a carpet, not matter how thick, may not be a particularly good insulator.

• Wear eye protection - large plastic lensed eyeglasses or safety goggles.

• Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts.

• Set up your work area away from possible grounds that you may accidentally contact. Do not work on a metal bench.

• Have a fire extinguisher rated for electrical fires readily accessible in a location that won't get blocked should something burst into flames.

• Use a dust mask when cleaning inside electronic equipment and appliances, particularly TVs, monitors, vacuum cleaners, and other dust collectors.

• Know your equipment: Electronic equiptment may use parts of the metal chassis as ground return yet the chassis may be electrically live with respect to the earth ground of the AC line. Do not assume that the chassis is a suitable ground for your test equipment!

• If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a 2 W or greater resistor of 100 to 500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K to 100K ohm resistor). Monitor while discharging and/or verify that there is no residual charge with a suitable voltmeter. Discharge to the metal chassis.

• Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations.

• If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand.

• Perform as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in a power supply section be tested for short circuits with an ohmmeter.

• Use an isolation transformer if there is any chance of contacting line connected circuits. A Variac(tm) (variable autotransformer) is not an isolation transformer! However, the combination of a Variac and isolation transformer maintains the safety benefits and is a very versatile device.

• The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but may not protect you from shock from many points in line connected equiptment, or the high voltage power supply. equipment.) Fuses and circuit breakers are to slow in many situations to provide any protection.

• Don't attempt repair work when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity.

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Last up-date 06/10/2004