"Three musts" for measuring the voltage of color tube filaments with a pointer multimeter

As long as the "three musts" principle is adhered to when measuring the filament voltage of color tubes, the filament voltage of various color TVs will be a unified fixed value.

First, the filament voltage must be measured directly. That is, it should be measured at the two pins of the filament of the tube holder, not at the two pins of the filament winding of the line output transformer. This is because the filament circuit of various color TVs has one (or two) resistors in series, with different resistance values, some are 3.9Ω, some are 1Ω... The voltage output of the filament winding of the line output transformer of different color TVs is different, and it is by connecting current limiting resistors of different values ​​in series that the voltage drop of the filament meets the requirements.

Second, the measurement must be done twice. The two test leads must be swapped for the second measurement. Assume that the red pen is connected to pin A and the black pen is connected to pin B in the first measurement. This will result in two different voltage readings. Try calling the higher reading "large value" and the lower reading "small value". Here, it is stipulated that the filament voltage refers to the large value. Why are the two measurement results different? Because the line pulse is directional, and the AC voltage range of the multimeter happens to use a half-wave rectifier circuit, so the two measurement results are different, with a difference of about 0.6V.

Third, you must use your own multimeter with the AC 10V block. According to this measurement principle, we can determine the standard value of the filament voltage (maximum value). For example, the author used the AC 10V block of Nanjing Jinchuan 47 multimeter to measure on multiple 14-21-inch color TVs, and the filament voltage (maximum value) was 4±0.2V. In actual measurements, regardless of the diameter of the color tube or the size of the screen, the normal reading of the filament voltage is 4±0.2V.

With the above-mentioned "three musts" principle, every repairman can obtain the "standard value" of the normal color TV filament voltage without changing the meter or shifting gears. This measurement method is simple, practical and easy to master.