THE TELEVISION MONITOR
One of the major tools used in video repair is the analog color monitor. Therefore it is paramount that it deliver an accurate color picture every time. Broadcast monitors are adjusted just like a VCR by using test instruments, signal inputs and screen samples. Because it is the eyewitness to performance it has to be right. Professional analog monitors can be switched to handle the input from the VCR in different ways. In addition to regular contrast and color, image centering and synchronizing adjustment can be done. Common things that are looked for during testing are dot crawl, color over-modulation, picture noise and color bleeding. The pattern seen above is the NTSC* color bar standard set by the SMPTE (Society of Motion Picture and Television Engineers). In addition to checking for color correctness and saturation it is also used to set a white level. The bars are arranged in a progression from left to right with gray having a set value of 75%. The black and white areas on the bottom help gauge the amount of gray. After the gray bar there are six color bars. This monitor can generate its own color bar signal as a test comparison to an incoming signal. Only three of those colors can be faithfully produced by a television. These are the primary colors of light, red, green and blue. They are represented in the pattern. The other three colors are a mixture of these primary three. They can cause difficulty when being generated by a monitor or VCR. Yellow is the most difficult. To see why examine the additive (light) method in the illustration below to see that it is made by mixing green and red light.  Yellow has a tendency to be dull because of the chemical and physical difficulty in making LEDs and the tube-type television guns that can produce pure primary colors. You add too much of either red or green and yellow changes shade or gets too bright and turns white. The next most difficult to make is magenta. Because it is made with blue, which is the darkest of the primary colors, it tends to be hard to keep clean. Any minor deviation in the signal tends to make magenta a little noisy. In the real world this is tolerated because a picture is seldom made up of only magenta. The color cyan has the same issue as magenta except both green and blue are dark colors. Only a little noise shows up in cyan. For comparison next to the light additive chart is one for mixing pigments (paint) called the subtractive method. When the VCR faithfully reproduces this SMPTE pattern within given parameters it is working at its best. After every repair, reconditioning or refurbishing I record this pattern and include the cassette with the VCR. The picture in the monitor is representative, one this clean only comes from test equipment. Click the picture above and you will see the resolution test pattern that checks the sharpness and the color detecting circuit. It is known as the resolution chart. Both the monitor and the VCR must switch from color to black and white and this screen tests that ability. It is also used for adjusting the focus and it has line resolution gradients used for checking sharpness. This also illustrates the maximum lines of resolution the monitor can produce, which is 500 for analog broadcasting. When this pattern is played back using a Betamax the picture is not going to be as sharp as the test screen. SuperBeta can do 320† lines of the original 500 lines. Fewer lines means less definition and the picture becomes softer and less distinct. This test pattern also checks picture uniformity. The circles must be perfectly round and the lines straight. The VCR has no part in this. It only passes the picture through as received and is not responsible for the size and shape. (Note: the Beta VCRs that can produce a stored digital image do have adjustments for controlling the placement, size, color, etc.)†† Click to the next screen. This is black and white pattern called the indian head and it checks the brightness and contrast. The next and last pattern, called the splash, because it hits all the areas of picture reproduction. It contains elements of the other three in one screen. The monitor that I use is consistent at producing a good picture with true accurate colors, and it is an indispensable tool. *NTSC is an acronym for the National Television System Committee. They are responsible for the analog television color system that was introduced in North America in 1954 and stayed in use until digital conversion. It was one of three major analog color television standards used in other countries. They are called PAL and SECAM. To go to the other subjects covered in this section:
 s speed can go over 360 lines. Extended Definition Beta can do well over 550 when using metal tape. Note: The standard analog broadcast picture is set at 550 lines. But you are only shown 500. Those left over fifty lines are hidden at the top and bottom of the screen and are reserved for some secret signals used by the television, tuner and VCR. One could conclude the the VCRs are actually capable of doing higher numbers if you include these hidden lines. The models that can record Super Hi-Band s 6.0 are the s. When Sony started making only SuperBeta models most would play the 5.6MHz but not record it. Click on the model numbers to see that VCR in the browser. To bring the refurbished page back to the browser window click here.†† There are a number of late model Betas that use digital image storing in one form or another. They are the ©Misterßetamax go to homepage |
