Horizontal Amplitude Control - Mitsubishi DPLUS 74SB -BKA Service Manual

5. Horizontal amplitude control

Circuit Diagram
Circuit Description:
Q1
1) Diodes D1 and D2 compose the bipolar modulation circuit, and have the function of controlling the
currents of the coils 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 transistors Q2 and Q3
compose the Darlington current amplifier, and the operational amplifier U1 composes the emitter-coupled
circuit, that stabilizes the voltage and controls 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 = 1.91 to 4.06V
A
V CENTER: 31 to 64 kHz = 11.6 to 27.4V
M
B+
DY
CT
D1
CS
Lm
Cm
D2
Csm
Therefore, Vcs = (ly * Ly)/ts
π
*Ts), Tr = LyCt , Tm =
↑ →
+28V
Q2
Q3
Vb1
Vm
→
ly = (Vcs * ts)/Ly, with B+ fixed.
↓ →
Vcs
LmCm )
↓ → ↑ →
VbI I1 I2
7-34
I1
+
-
U1
↑ → ↓ → ↓
Vc ly
↑ → ↑
ly
↑ → ↓ →
Vm . An inference in
H-Width
Va