NEC MultiSync FP1370 Service Manual page 138

E/W from IC501
(H)
H_Drive
Pulse
H.SIZE MAX
＋
H.SIZE
①Horizontal size modulation circuit
The transistor Q5A1modulates the Chopper output voltage that location is C5G3. This transistor is biased
by R5AC and R5AE and the modulation wave is added to the base through C5A6. The modulation wave
is made by Horizontal size correction circuit which is described section 2).
②User H SIZE control
OSM control for users vary from 0 to 255. At this time, the voltage of IC532 pin 5 (HS control line) vary
from 5V to 0.9V.
The horizontal video size reduces as much as approximately 78% irrespective of the horizontal frequency
when the maximum size is taken to 100%.
③H SIZE MAX control
The H SIZE MAX control is accessible in service mode only, and this control sets the maximum horizontal size.
The H SIZE for user control vary from the horizontal maximum size which is adjusted at this stage to less than
the H SIZE MAX. H SIZE MAX control vary from 0 to 255 on OSM menu, and the voltage of IC532 pin 6
output voltage vary from approximately 0.9V to 5V. The horizontal maximum size control voltage (HSM)is
output to IC591 pin 10 and is compared to the HS voltage (IC591 pin 9) . The HSM output voltage is
converted to slice voltage at the comparator for PWM control which is input to error amplifier IC592 pin 1.
(V)
220V
C598
R59J
(H)
3 2
8
SAW GEN
Error Amp
Ref.
6
Voltage
1 13
IC591
(Fig. 2.9) HORIZONTAL SIZE CONTROL CIRCUIT
Amplifier
IC5GA
PWM Chopper
Q5G1
9
PWM Amp
Bufferr Amp
IC592
4 5
FB
＋
AFC_Feedback
8-13
+B Modulator
Q5A1
(H)
+B
H.Out Trans
H.Def Out
(V)