Fbt Secondary & Dynamic Focus - NEC N9902-1 Service Manual

(c)Horizontal linearity compensation circuit:
(1)The main component is that L303 is Linearity coil and L302 is choke, when the horizontal < 52K
only L301 on and L302 off, when the horizontal > 52K, L301, L302 all on. Compensation circuit is
consists of L301, L302, RL301 and Q322.
(2)The control voltage is from U701 pin 30, it varied with horizontal frequency. When the horizontal
frequency > 52K, U701 pin 36 output voltage is high and L302 is on, the horizontal frequency <
52K U701 pin 30 output voltage is low and the L302 is off.
(3)C344 is the Cs capacitor, and Q324 controls C345, Q326 controls C347, Q325 controls C346,
Q327 controls C348. The U701 pin 1, 2, 3, 4 controls the Q324, Q326, Q325 and Q327
respectively. So different frequency has different combination to meet the requirement.
FH < 30K
30K < fH < 34K
34K < fH < 36.5K
36.5K < fH < 45K
45K < fH < 52K
52K < fH < 62.5K
62.5K < fH < 67K
67K < fH < 74K
74K < fH < 83K
83K < fH < 96.5K
96.5 < fH
6. FBT Secondary & Dynamic Focus
(a)Focus and screen voltage are come from FBT bleeder.
(b)G1 bias is controlled through R399, VR304, R308, R30K, R30F, Q323 and Q331.
(c)Q329 is controlled by MCU pin 31 Mute 2, and it will blank the picture during mode change.
(d)Q401 is the blanking buffer to G1 to blank the retrace line of picture.
(e)R318, R322, R305, D302, ZD301, Q339 and Q340 are the x-ray protection circuit. Once the HV rises
abnormally, U301 win shut down itself, all the horizontal deflection is stopped by then.
(f)Dynamic Focus:
(1)H-Focus: U301 pin 10 outputs a parabolic waveform and through Q302 into Q338 to get a reverse
amplified waveform. This waveform is through the SEPP Q303 and Q304, as a current gain then
input into T303.
(2)V-Focus: U401 pin 5 output waveform through R329, C322, R32G and C324 to get a parabolic
waveform. This waveform is amplified by Q305 and input into T303.
(3)H-Focus and V-Focus are into T303 to get a combined waveform that will input to FBT.
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Cs Table By Frequency
CS1
0
0
0
0
1
1
0
1
1
1
1
29
CS2 CS3
0 0
0 0
0 1
1 1
0 0
1 0
0 1
0 1
1 1
1 1
1 1
CS4
0
0
0
0
1
1
1
1
1
1
1