Hv Regulation / Raster Centering / Hv Circuit / Dynamic Focus Circuit Operation; Hv Regulation - Hitachi 36SDX88B Service Manual

10. HV Requlation / Raster CenterinqlHV Circuit/Dynamic Focus Circuit Operation
10.1 HV Regulation
HV regulation is done by applying the divided voltage of THOI high voltage to QHl2, QH13 transfer the voltage
change to IH02 pin
#-I to regulate
the HV depending on the brightness of the picture.
The HV stabilized by modulating the HV drive pulse width to control the ON/Off switching of QH02.
If the picture goes bright, the HV falls then QH12 turns on and the voltage at QH13 is applied to IH02 pin (1)
connected to the internal error amplifier which compares it to a reference voltage at pin (14). The voltage at
pin (12) drops and the internal comparator changes to change the width of the output pulse voltage. The ON
time of QH02 becomes longer to stabilize the HV.
10.2 Raster Centering Circuit
R741 adjust raster position by changing Q711 (B) and Q712 (B) voltage. The output voltage flows through L708
to L707 (linearity circuit) in series with H. DY coil to shift the center by changing its bias.
HV Regulation
CH33
+t =
m
DH27
;0/50
xxx
CE-hi
OH24
RH77
JH06
DFMiSA4
4.7KIiXI
0-u
u -
RI-MO
390K
RH74