51 How Often to Degauss:
Description
This article is from the comp.sys.ibm.pc.hardware.video Frequently Asked Questions, by Michael Scott with numerous contributions by others. (v1.0).
51 How Often to Degauss:
Some monitor manufacturers specifically warn about excessive use of degauss, most likely as a result of overstressing components in the degauss circuitry which are designed (cheaply) for only infrequent use. In particular, there is often a thermister that dissipates significant power for the second or two that the degauss is active. Also, the large coil around the CRT is not rated for continuous operation and may overheat.
If one or two activations of the degauss button do not clear up the color problems, manual degaussing using an external coil may be needed or the monitor may need internal purity/color adjustments. Or, you may have just installed your megawatt stereo speakers next to the monitor!
You should only need to degauss if you see color purity problems on your CRT. Otherwise it is unnecessary. The reasons it only works the first time is that the degauss timing is controlled by a thermister which heats up and cuts off the current. If you push the button twice in a row, that thermister is still hot and so little happens.
One word of clarification: In order for the degauss operation to be effective, the AC current in the coil must approach zero before the circuit cuts out. The circuit to accomplish this often involves a thermister to gradually decrease the current (over a matter of several seconds), and in better monitors, a relay to totally cut off the current after a certain delay. If the current was turned off suddenly, you would likely be left with a more magnetized CRT. There are time delay elements involved which prevent multiple degauss operations in succession. Whether this is by design or accident, it does prevent the degauss coil - which is usually grossly undersized for continuous operation - to cool.
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