Ramsey Electronics PG13 Instruction Manual page 6

greater resistor of 100-500 ohms/V approximate value (e.g., for a 200 V
capacitor, use a 20K-100K ohm resistor). Monitor while discharging and/
or verify that there is no residual charge with a suitable voltmeter. In a TV
or monitor, if you are removing the high voltage connection to the CRT (to
replace the flyback transformer for example) first discharge the CRT
contact (under the insulating cup at the end of the fat red wire). Use a
1M-10M ohm 1W or greater wattage resistor on the end of an insulating
stick or the probe of a high voltage meter. Discharge to the metal frame
which is connected to the outside of the CRT.
•
For TVs and monitors in particular, there is the additional danger of CRT
implosion - take care not to bang the CRT envelope with your tools. An
implosion will scatter shards of glass at high velocity in every direction.
There is several tons of force attempting to crush the typical CRT. Always
wear eye protection.
•
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 the power supply section
of a TV or monitor can 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.
See the document "Repair Briefs, An Introduction", available at this site,
for more details.
•
The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a
good idea but will not protect you from shock from many points in a line
connected TV or monitor, or the high voltage side of a microwave oven,
for example. (Note however, that, a GFCI may nuisance trip at power-on
or at other random times due to leakage paths (like your scope probe
ground) or the highly capacitive or inductive input characteristics of line
powered equipment.) A fuse or circuit breaker is too slow and insensitive
to provide any protection for you or in many cases, your equipment.
However, these devices may save your scope probe ground wire should
you accidentally connect it to a live chassis.
•
When handling static sensitive components, an anti-static wrist strap is
recommended. However, it should be constructed of high resistance
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PG13 6