Horizontal Amplitude Control - NEC MultiSync 75F-3 Service Manual

5.

Horizontal amplitude control

Circuit Diagram
Q1
Description of the circuit:
1) The diodes D1 and D2 compose the bipolar modulation circuit, and have the function of controlling
the currents of the oils DY(lpp) and Lm(lm) through voltage modulation carried out by utilizing VM.
B+ = Vm +Vcs
Such being the case, the horizontal width decreases when Vm
Inversely, the horizontal width decreases when Vm
(B+ = (Vp*2Tr)/(
2) Q2, Q3 and U1 compose the control circuit of H-WIDTH. Of those devices, the transistor Q2 and Q3
compose the Darlington current amplifier, and on the other operational amplifier U1 compose the
emitter-coupled circuit, that stabilize the voltage and control the current.
3) The horizontal width broadens when Va
the opposite sense is also possible.
Test points for maintenance:
1) C = 31 to 37 kHz = 3.2 us
T
48 to 64 kHz = 3.0 us
÷
Cm 2.8 us
2) V CENTER: 31 to 64 kHz ¡Ü
A
V CENTER: 31 to 64 kHz ¡Ü
M
B+
DY
CT
D1
CS
Lm
Cm
D2
Csm
Therefore, Vcs = (ly * Ly)/ts
π
*Ts), Tr = ¡Ô ¡ÔLyCt, Tm = ¡Ô
¡Ô
¡Ô ¡Ô
¡Ü 1.91 to 4.06V
¡Ü
¡Ü ¡Ü
11.6 to 27.4V
¡Ü
¡Ü
¡Ü ¡Ü
+28V
Q2
Q3
Vb1
Vm
→
ly = (Vcs * ts)/Ly, with B+ fixed.
↓ →
Vcs
¡Ô
¡ÔLmCm)
¡Ô ¡Ô
↑ → ↓ → ↑ →
VbI I1
70
Va
I1
+
-
U1
↑ → ↓ → ↓
Vc ly
↑ → ↑
ly
↑ → ↓ →
I2 Vm . An inference in
H-Width