How to discharge CRT television tube

When working on electrical equipment it is important to think safety first and in case you are working on CRT television there are areas where a technician both a novice or an experienced one should be on high alert because of high current and voltage around those places.

One area you should not work when tired or working on late after others have slept is the power supply if you are doing voltage testing (live). If the power is off just be sure the main capacitor is discharged by doing a quick voltage test across this capacitor with power off and the equipment disconnected from the power outlet.

To Discharge the Main Capacitor you can use this gadget which I introduced to you on solving smps problems elsewhere on this blog.

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Usually the main capacitor discharges after a few seconds but there could be a problem in the circuit which can cause it not to discharge…one of the reason why  the main capacitor is not discharged could point to an open start up resistor-These resistor also act as bleeder resistors for the main capacitor.

Another area where Technician needs extra care is the CRT tube anode cap, this can still hold charge long after the Television has been removed from the power source and therefore if for any reason you want to remove the Anode cap(clip) from the Tube it is important to discharge the tube first and must be done after disconnecting the Television from the power outlet.

Perhaps I can point out here that even though the voltage is very high(around 24kv to 30 kv) the current is very small and therefore one can use the meter probe between the Anode cap(clip inside) and the crt ground as shown in the diagram below.

Please be sure to disconnect the Crt ground return to the Television chassis ground.

Let meet in the next class

  

Humphrey Kimathi

Author CRT television repair course