1981 Magnavox with a problem.

[jr_tech]

Originally Posted by Jeffhs

To discharge the tube, simply slide a metal screwdriver under the cap covering the high-voltage lead coming from the flyback. Remember that the HV charge on a CRT can remain on the tube for quite a while after the set is turned off, even if it has been unplugged and unused for years.

Hopefully that is a GROUNDED screwdriver!

jr

[Jeffhs]

Originally Posted by jr_tech

Hopefully that is a GROUNDED screwdriver!

jr

I stand corrected. Yes, a grounded screwdriver should be used to discharge the residual HV charge on a CRT; I've been in electronics (as a hobby) and in ham radio 40 years, and should know that.

This is a good warning for newcomers to tube TV repair, however, as folks who have only known solid-state and, particularly (since the mid-'80s) flat-screen TVs may not be aware of the dangers of the redsidual charge on the CRT bell on old analog NTSC TVs -- even after the set has been unused for some time. The aquadag coating on the CRT bell acts as a huge capacitor and can hold a charge for a very long time, so discharging the tube by using a grounded screwdriver slid under the second anode cap until it contacts the terminal which connects to the 2nd anode well on the side of the tube is a must, before any work is begun on the chassis. (I would discharge the CRT even before changing tubes, as some older TVs had some tubes located near or directly under the CRT bell; I've owned a few -- my Philco Microgrid 390 23" console, now long gone, of course, comes to mind.)

Again, the voltage coming from the flyback in all CRT televisions is extremely high (20kV+ in color sets) and can cause serious injury or even death, so be careful. The voltage on LCD or plasma panels in today's flat TVs is nowhere near that high (several hundred volts at most), but, nevertheless, caution should be used around them as the potential for serious injury still exists.