Beijing card 8320 - 3 model color television is Tianjin communication Broadcasting Corporation the product at the beginning of 90 time, it is in 8320 - 1 model video N increased to control decipher function on the foundation of color television.
This model the change-over circuit making type of machine is it is core in order to make LA7950 of type identifying integrated circuit, add a few outside receive component, use IC) of decipher of μ PC1423CA(color embedded make compatible NTSC make part of lubricious decipher circuit comprise with PAL. It can be divided roughly identify circuit and circuit of control of the changeover that make type to make type two parts.
1  makes type identifying circuit: Form for the center with LA7950, identify a result to bring crural output to dominate relevant circuit accordingly by its with the means of tall, low n. LA7950 in-house block diagram and the function that cite a base is shown 1 times like the graph, its work normally voltage is tagged see a picture 2. Working principle summarizes as follows: R13 of classics of travel retrace pulse, R12 and C11 coupling come N011 foot, send internal tension comparator, the extent of this pulse asks to be in 8 ～ of 4  between 5  8V. The fiducial voltage of voltage comparator is the classics of ＋ 12V voltage that carries 2 feet place to add by power source after internal resistance cent is pressed, get. After plastics of comparator of voltage of classics of travel retrace pulse, get tally place needs spark pulse, right now video signal also comes via block is being received to allow component coupling outside N014 foot in-house and synchronous detached circuit, get signal of synchronism of compound travel, field thereby, this signal is outputted by 3 feet, the depart after the integral circuit that comprises via R16, C13 again comes on the stage synchronous signal, this signal sends to the tally of N015 foot interior via C12 and R17 again, regard its as restoration pulse, namely on the spot when synchronous signal comes, tally restoration, so that cipher out has pulse of how many travel inside cycle of a field, final result sends judgement circuit to undertake a frequency identifying. If one have 240 ～ inside field,287 go pulse, decide for 60Hz, make for NTSC, right now 7, 8 feet show tall n namely 12V, 9, 10 feet show low n namely 0V; If one have 288 ～ inside field,340 go pulse, decide for 50Hz, make for PAL, right now 7, 8 feet show low n, 9, 10 feet are tall n.
2  make type change control circuit: Of N01 7, 8, 9, 10 each feet are received respectively to periphery of N201(μ PC1423CA) in corresponding circuit. By the graph 2 knowable, the output signal cent of N017 foot is two: Send to the N that comprises by R428, R429 and VD424 to make all the way adjust circuit; Send to the N that comprises by RP252, VD281 to make hue adjust circuit all the way, this two parts all output the ability when tall n to act well in N017 foot. R25 of classics of N018 foot signal is received carry to switch control of N201{26} foot P/N, control the decipher circuit job with N201 corresponding interior thereby. Signal of N019 foot output divides as much it is two: Send to PAL all the way hue adjustment circuit; Receive the subcarrier brilliant to N201{20} foot periphery all the way brace up control circuit, because circuit is simpler,detailed fine workmanship makes a process no longer give uncecessary details. N0110 foot is received to N201{44} foot external 3  58MHz absorbs circuit XT, when working to be made at N, 10 feet show low n, XT absorbs circuit to divide filter of signal of chroma of 3  58MHz, disturb luminance signal in case.
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