Service manual

STP 11-25R13-SM-TG
S - 17
c. As previously stated, color television programs must be transmitted so they can be faithfully
reproduced by present black and white receivers without any modifications. This feature is known as
compatibility (Figure S-15).
Figure S-15. Compatibility
S-17. Reverse Compatibility.
Black and white reception on a color receiver is the next requirement. A black and white signal
transmitted by a monochrome system is split three ways and is applied to the red, green, and blue
electron gun cathodes of the color CRT.
a. Before this signal is applied to its electron guns, the CRT is adjusted to produce a white raster.
b. After a white raster is obtained, the signal is applied to all three guns and the black and white
signal being transmitted produces a monochrome picture. In the process of producing a white screen,
the electronics of the CRT automatically separate the brightness signal into the ratio of 30 percent red, 59
percent green, and 11 percent blue as the signal is applied to the electron guns. Figure S-16 shows
reverse compatibility.
Figure S-16. Reverse Compatibility