Abstract:
A method and an apparatus that verify the correct operation and calibration of a wobbling coil CRT monitor landing adjustment jig. The video test signal and the wobbling coil signal are disconnected from the CRT under test. The invention receives the video test signal and the wobbling coil signal and generates a modulated video test signal by modulating the video test signal with the wobbling coil signal. The modulated video test signal simulates a correctly adjusted CRT or a CRT with a known amount of misadjustment regardless of the actual state of adjustment of the CRT under test.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to the manufacture of color cathode ray tubes (CRTs), and more particularly to the adjustment of deflection yokes on CRTs, and most particularly to the calibration of test fixtures used to adjust deflection yokes on CRTs. 
     2. Background Information 
     A color CRT has red, green, and blue phosphors on the inside face. These phosphors produce red, green, and blue light when struck by an electron beam. Three electron guns are used to produce red, green, and blue images which are perceived as a full color image. 
     Each of the different colored phosphors is precisely placed on the face of the CRT and is separated from adjacent colors by a carbon strip that does not produce light when struck by an electron beam. The electron guns must be adjusted so that they accurately strike the appropriately colored phosphors to produce a high quality image. 
     In particular, the electron guns must be adjusted so that the full diameter of the electron beam falls on the phosphor rather than the carbon strip to produce maximum luminance. This adjustment is termed a landing calibration. Every dot on the screen is subject to a landing miscalibration and the landing calibration requires that the deflection yokes be adjusted to minimize the overall miscalibration. 
     Some CRT designs control each electron gun with a separate deflection yoke necessitating landing calibration of each yoke. Other CRT designs, such as the Sony Trinitron®, use one deflection yoke to control all three electron guns and only a single landing calibration is required. Some CRT designs use phosphor dots and both a vertical and a horizontal landing adjustment are required. Other CRT designs, such as the Sony Trinitron®, use vertical phosphor strips and only require a horizontal landing adjustment. 
     A landing adjustment jig can be used to adjust a deflection yoke. One such landing adjustment jig employs wobbling coils clamped around the neck of the CRT to deliberately shift the electron beams in response to a wobbling coil signal. The wobble causes the screen to get brighter and dimmer as the electron beam is swung through the point of being properly landed. Optical sensors check the luminance of the CRT under test at a plurality of points distributed over the face of the screen. The CRT is in calibration if the landing miscalibrations are minimized, as indicated by maximum luminance, when the wobbling coil signal is zero. 
     The landing adjustment jig is very sensitive and is able to detect landing offsets, mislandings, as small as 0.1 micron at each point on the CRT that is tested. The problem is that it is difficult to verify that the landing adjustment jig is functioning properly. What is needed is a way to verify the proper operation and accuracy of a landing adjustment jig. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and an apparatus that verify the correct operation and calibration of a wobbling coil CRT monitor landing adjustment jig. The invention receives a wobbling coil signal and a video test signal from the landing adjustment jig. The wobbling coil signal and the video test signal are disconnected from the landing adjustment jig while the invention is used. The invention modulates the received video test signal with the wobbling coil signal to produce a video test signal which is connected to the CRT under test to produce maximum luminance on the CRT under test at the time when the wobbling coil signal is such that a properly adjusted CRT under test would produce maximum luminance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a block diagram of a prior art CRT and landing adjustment jig. 
     FIGS. 2A,  2 B, and  2 C illustrate various landing conditions of an electron beam on a prior art CRT. 
     FIG. 3 illustrates a block diagram for an embodiment of the invention connected to a prior art CRT and landing adjustment jig. 
     FIG. 4 illustrates a block diagram for an embodiment of the invention. 
     FIG. 5 illustrates electrical wave forms for an embodiment of the invention. 
     FIG. 6 illustrates electrical wave forms for another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     A method and apparatus for verifying the correct operation and accuracy of a landing adjustment jig using wobbling coils is described. The described method and apparatus receives the wobbling coil signal and the video signal for the electron beam being adjusted and modulates the intensity of the video signal to simulate the effect of the wobbling coil. The wobbling coils do not receive the wobbling coil signal during the calibration procedure. The described method and apparatus allows the operation and calibration of the landing adjustment jig to be verified regardless of the landing adjustment of the CRT connected to the landing jig for the verification. 
     FIG. 1 illustrates a prior art CRT under test  100  in a prior art landing adjustment jig. The landing adjustment jig is comprised of a signal generator  110 , wobbling coils  120 , a control box  130 , and an optical sensor  140 . The signal generator  110  supplies video signals  112 ,  114 ,  116  to the CRT under test  100  to generate a maximum luminance, monochromatic display. The wobbling coils  120  are clamped to the neck of the CRT under test  100 . The control box  130  generates a wobbling coil signal  132  which causes the wobbling coils  120  to shift the electron beam of the CRT under test  100  through a range of landing offsets. The optical sensor  140  senses the luminance at a number of locations on the face of the CRT under test  100 . The luminance information  142  is transmitted to the control box  130  where it is compared to the wobbling coil signal  132 . Maximum luminance at a zero wobbling coil signal  132  indicates that there is no landing offset. 
     FIGS. 2A,  2 B, and  2 C illustrates various landing conditions on a prior art CRT having vertical phosphor strips  200 . The phosphor strip  200  is between two carbon strips  210 . FIG. 2B illustrates a correctly calibrated landing condition. The electron beam  230  falls entirely on the phosphor strip  200  creating maximum luminance. FIG. 2A illustrates a negative landing offset. Part of the electron beam  220  falls on the carbon strip  210  before the phosphor strip  200  resulting in reduced luminance. FIG. 2C illustrates a positive landing offset. Part of the electron beam  240  falls on the carbon strip  210  after the phosphor strip  200  again resulting in reduced luminance. 
     FIG. 3 illustrates an embodiment of the present invention connected to the prior art CRT under test  100  in the prior art landing adjustment jig. The wobbling coil signal  132  is disconnected from the wobbling coils  120  and connected to the landing calibration checker  300 . The wobbling coils  120  are left unconnected during the calibration. The video signal  112  for the electron beam under test is disconnected from the CRT  100  and connected to the landing calibration checker  300 . The landing calibration checker  300  rectifies the wobbling coil signal  132 , which modulates the video signal  112 , to generate a modulated video signal  302 , which is connected to the CRT  100  in place of the disconnected video signal  112 . 
     FIG. 4 illustrates a block diagram for the subsystems of an embodiment of the present invention which corresponds, as a whole, to the landing calibration checker  300  of FIG.  3 . FIG. 5 illustrates electrical wave forms for selected signals in the landing calibration checker  300 . 
     The wobbling coil signal  132  is received by the wobble signal receiver  400 . The wobbling coil signal  132  is shown as wave form A in FIG. 5. A conditioned wobble signal  402  is transmitted from the wobble signal receiver  400  to the rectifier  410 . The rectified wobbling coil signal  412  is shown as wave form B in FIG.  5 . 
     The video signal  112  is received and conditioned by the video signal receiver  420 . The conditioned video signal  422  is modulated by the rectified wobbling coil signal  412  in the modulator  430 . The modulated video signal  302  is transmitted to an electron gun of the CRT under test  100 . The modulated video signal  302  is shown as wave form C in FIG.  5 . It is significant that the maximum amplitude of the modulated video signal  302 , which will produce the maximum luminance of the CRT under test  100  regardless of the CRT&#39;s landing offset, occurs at the point of the zero amplitude wobbling coil signal  132 . If the landing adjustment jig is functioning properly, maximum luminance of the CRT under test  100  at the point of the zero amplitude wobbling coil signal  132  will be interpreted as a correctly adjusted CRT. If the CRT is not reported as being correctly adjusted, then a malfunction of the landing adjustment jig is indicated. 
     In another embodiment of the present invention, the wobble signal receiver  400  comprises user controls  134  that allow a bias voltage to be combined with the wobbling coil signal  132  to simulate a predetermined degree of mislanding by the landing calibration checker  300 . FIG. 6 illustrates electrical wave forms for selected signals in a landing calibration checker  300  where a bias voltage has been applied. The effect of the bias voltage is represented by line V B  on wave form A of FIG.  6 . The effect of the bias voltage is to shift wobbling coil signal  132  so that line V B  is the zero voltage line for the biased wobble signal  402  that is transmitted to the rectifier  410 . The rectified biased wobbling coil signal  412  is shown as wave form B in FIG.  6 . The modulated video signal  302  that results from the bias of the wobbling coil signal  132  is shown as wave form C in FIG.  6 . 
     It is significant that the maximum amplitude of the modulated video signal  302 , which will produce the maximum luminance of the CRT under test  100  regardless of the CRT&#39;s landing offset, now occurs at a point where there is a known non-zero amplitude wobbling coil signal  132 . The known non-zero amplitude wobbling coil signal  132  corresponds to a determinable landing offset. The use of a bias voltage to create a maximum luminance at a known non-zero amplitude wobbling coil signal  132  allows the landing adjustment jig calibration for measurement of landing offsets to be verified. 
     In particular prior art landing adjustment jigs, the wobbling coil signal  132  is not a sawtooth wave form as described above and shown in the accompanying drawings. It can be a triangle wave, stair step wave, sine wave, or other wave form without affecting the function of the present invention. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.