in channels operating at the designated frequency after synthesizing the correct channel frequency athe microcomputer looks at afc discriminator information from which local oscillator tuning voltage direction is determined to achieve automatic fine tuning the tuning voltage is then stepped by the microcomputer in small frequency increments which vary from 28 khz for channel 2 to 80 khz for channel 80 in the direction of the desired frequency until the center video carrier frequency is passed the tuning voltage is then returned to the preceding step to which frequency the receiver is then locked with essentially all broadcasting stations operating at or very close to the fcc designated frequency highly accurate tuning to the selected channel is thus permitted video carrier verification is accomplished by microcomputer analysis of afc discriminator and vertical sync states the tuning system is described and claimed in referent copending application ser no 107 732 the microcomputer is a four bit e d mos unit with a read only memory a random access memory an arithmetic logic unit input output ports and a clock generator all on a single semiconductor chip the microcomputer chip is one of the mn1400 series basic design as manufactured by matshushita electronics corporation and especially modified for the referent 39 732 application switching logic section 90 is an elementary logic unit that responds to the means for sensing the raised and lowered positions of screen 24 for stopping and reversing motor 74 at the respective positions it responds to pulses from the microcomputer and emits command logic pulses and also has other elementary logic circuit functions as will be described screen up relay 92 and screen down relay 94 provide for.