Secrets To Discharge Capacitor That All Electronic Repairers Should Know
Capacitor discharge is the first thing you should do as an
electronic repairer before touching the power supply section. The large filter capacitor in the power supply section can hold dangerous high
voltage even if the unit has been off for few days. It is advisable to discharge the filter capacitor first before you start to troubleshoot
in order protect yourself from electrocuted. Though the capacitor current stored in the capacitor can’t kill you but it is enough to burn your
hand, fingers and your skin when you accidentally touch it and the worst case is while you’re carrying the Monitor or TV, you might just throw
off the equipment when you got a shocked from the filter capacitor and the cathode ray tube monitor may break and cause the flying glasses to
hit your body or eyes.
Just be cautious when handling the power supply area. You can
always use a meter to confirm whether there is still charge in the capacitor. Place your meter’s black probe to the capacitor negative pin
(you can see the negative marking at the sleeve of the capacitor) and the red probe to other pin. If there is high voltage registered in your
meter then you have to discharge the capacitor otherwise you may proceed to repair the equipment. Typical value for this type of filter
capacitor is 220 to 330 microfarad with a 400 to 450 voltage rating.
The large filter capacitor in power supply section
There are three ways to discharge the large filter capacitor in a switch mode power supplies.
Discharging the capacitor with a screw driver (not recommended).
The reason for not using the screw driver to discharge a capacitor is because the printed circuit board or circuitry can be damaged due to
the spark generated while discharging the high voltage in the capacitor. I once have blown the power area using this method. However, if you knew
that the capacitor stored voltage is not too large after confirmed it with a meter, you can easily discharge it with a small screw driver.
Just place the screw driver tip to touch the two pin of the capacitor, within seconds the charge will be gone. If
the capacitor holds a heavier charge of electricity then discharging the capacitor with a screw driver may melt the tip of the screw driver
and the copper on the printed circuit board. Sometimes a big spark may cause small disintegrated solder lead or copper to fly out from the
circuit board and might injured your eyes or body.
Another method is that you can use a socketed 100 watt electric light bulb and touch the two wires coming out from the light bulb on the leads of
the capacitor. This method had been used by many electronic repairers around the world for the light bulb will act as an indicator to see if the
capacitor still holds the charge. If there is a charge the light bulb will light and after discharged the light bulb will goes off. I still
preferred the third method because you have to use both hands to touch on the capacitor lead.
Use a resistor to discharge the capacitor leads
Third method and also my favorite method is to place the leads of a high wattage resistor on the leads of the capacitors you want to discharge.
You can use either a 1.8 k or a 2.2 kilo ohm 5 to 10 watt resistor to discharge the high voltage capacitor in a switch mode power supplies. It is
very simple to use and very effective .It takes only a couple of seconds to fully discharge the capacitor.
Using only one hand, you can do the job while the other hand you
still can hold a solder gun or secure the equipment casing.
I strongly recommend to those who are using the screw driver to discharge a capacitor in power supply to consider the second and third method as
these is the safest methods. It not only protects the circuit, it also protects you. If you had discharge the capacitor and you are still not
sure or no confidence whether the charge already gone, you can always use a meter to confirm it.