Wednesday, December 29, 2010

【 Weak current College 】 about degaussing resistance interference color image of 】



1. degauss remaining current

Degaussing resistance into hot, degaussing coils still surviving certain level of micro-currents, called degaussing remaining current (or leakage current). Remaining current contains a variety of frequency components for picture interference problems buried foreshadow.

2. Why is degaussing remaining current interference

Degaussing the reason left in the current form, there are two ways:

(1) the remaining in the degaussing coil current direct interference grating. To pass the degaussing coils left current posted on the screen, you can see the grating, character very dazzling "shivering from". From the deflection angle of analysis, it is degaussing left degaussing interference by degaussing coil current produces a magnetic field, on a normal scan for errors. Native degaussing circuit so disturbing words, fruit of course even more serious.

(2) as a power clutter into power, thereby disrupting scans. Switching power supply anti-jamming capability bad, degaussing circuit tiny fluctuations can be left on the current power interference, thereby disrupting field scan circuitry, resulting in dark or black lines. Degaussing remaining current electricity, which is part of the emotional and the main current phase difference exists, will produce the degaussing coils induced voltage, this is it although weak but can interfere with the power of important reasons.

3. a three-legged degaussing resistance

Degaussing is the second left on the current leg degaussing resistance. To this end, and in the second leg degaussing resistance possession, posted a PTC auxiliary heating resistance (here called R η and degaussing resistance is called the R), thus forming a three-legged degaussing resistance. Compared with R, R Ŝ at room temperature value (more than 100 ohms). Large ambient temperature resistance R Ŝ then the initial heating current is small, the temperature to rise slowly, in a large current flows through the? R, rapid warming, R Ŝ also cannot afford heating function, and therefore does not affect the degaussing effects; R Ŝ temperature is high, you can let R Ŝ stability, completely blocking the degaussing remains current.

There is a three-legged degaussing resistance, degaussing interference problem finally solved? but some color using the three-legged degaussing resistance, interference but, and this is what causes? mainly PTC's parameters and manufacturing technology of two factors. If the temperature of the R Ŝ and RE, its auxiliary heating of significance is not great, not to mention there R Ŝ itself, so temperature fluctuation and two foot degaussing resistance differences are not large, interfering with the question of degaussing to highlight.

4. degauss interference relationship with scanning frequency

Why do some color (color display) on the remaining current interference degaussing particularly sensitive?

Scanning frequency difference is degaussing left and complete the picture interference.

To verify this assumption, do the following experiment: to a multi-system TV input signal, the screen will be VCD a degaussing coils series 2 foot degaussing resistance, power warm-up. When VCD signal-for PAI, degaussing coils on the TV screen, only the resulting screen, with the location moved to see it on screen. Pinned to the Soviet time on VCD signal to NTSC3.58 (field frequency 60Hz), degaussing coils a put, wriggle, description of the picture left current resulted degaussed apparent interference.

Conclusion: the color of the field in the scan frequency to and degaussing coils in remaining current in frequency (50Hz) consistent, there is no interference caused by jitter degaussing or flashing phenomenon; on the contrary, you may receive the degaussing interference, twist the screen is both frequency frequency.

Frequent press key to allow the degaussing open is degaussing, the resistor thermal test on the color display, found that when the resolution adjustment in 640/480 mode (row frequency 31.49Hz, field frequency 60.09Hz), or transferred in the 800/60 () mode (row frequency 38Hz, field frequency 60.32Hz), grating and screen are obvious sloshing and flashing; tune in 1024/768 mode (row frequency 6015Hz, field frequency 75.48Hz), the basic do not see the exception.

Conclusion: the monitor's normal field scan frequency with degaussing left current frequency (50Hz) difference is smaller, degaussing interference phenomenon is more pronounced.

5. degauss interference and horizontal dark band, black

Another degaussing interference phenomenon is a horizontal dark zone or horizontal black lines, its origin seems to be even more strange and unpredictable, the analysis seems more difficult.

We all know, the scan speed instantaneous change will cause the screen corresponding location shading, power ripple can cause field output current fluctuations, reflected on the screen is horizontal dark band or black lines (should be at the same time there is bright or brighter line), ripple on line scan modulation is grating left s-shape distortion.

According to this reasoning, degaussing left current noise since the with field scan frequency, with a certain part of instantaneous field scan speed also has a relationship.

Verify: assembling a degaussing circuit and fully preheating after degaussing coils on a 17-inch color display screen, you will see the screen just "shivering from" (800/600 mode), and no horizontal interference with or line.

At least three frequency signal control of electron beam scanning: deflection coil provides scan frequency (including certain parts of the transient abnormal scan frequency), degaussing remaining current 50Hz, degaussing remaining current in the Harmonic frequencies. The main factors caused by jitter is left in the current frequency and instantaneous scan frequency of "chance".

At this point, wecan generally know why some color and color display, use a good three-legged degaussing resistance without exception, the use of certain highly resistance to interference.

6. unexplained degaussing interference

Working with several manufacturers service peers talk was informed that the accident is degaussing often encountered, solutions are in accordance with the manufacturer's technical methods, degaussing coils plug parallel a few micro-method of capacitance and resistance substitution degaussing alone are often futile.


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