About Five Color Band Resistor
I came across many times in Monitor repair that the five band resistor had gone opened circuit. For your information, five band resistor value is more accurate than the four band resistor. With five band resistor you can get the value like 33.6 ohm, 47.2 ohm and etc. For the four color band resistor, the best value you can get are 33 ohm, 47 ohm and etc. In older design of Monitors you can actually see a small preset at the feedback circuit near optoisolator IC. This preset it tuned to set the B+ voltage to flyback transformer and if this circuit have problem or the preset fails (value run or dry contact), the high voltage will increase and shut down the Monitor.
So in order to prevent high voltage shutdown problem and made sure the B+ voltage is always stable, Monitor design engineers had placed a five color band resistor in place of the preset. With this fixed resistor in the feedback circuit, chances for the B+ voltage to shoot up is very slim unless the five band resistor itself have turned into high ohm or totally open circuit! In some cases, it was very difficult for me to get the exact resistance value (for a five color band resistor) thus i used the series resistance formula to help me get the value that i wanted. Isn’t it fun to do electronic repair work?
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