Power Source - Sharp PC-1211 Service Manual

- ----- -3.9V
VDISP
VB
------ -2.lV
- - - --- -3.9V
L_
VM
-------IV
...._ __ - - - --- - 2.8V
6.8ms----
VA
-- --- ov
...._ __ - - - --- -I.8V
11
Eye position
30°
o Adjustments of reference voltage VD ISP
The VDISP had been precisely adjusted to become -3.74V at an
ambient temperature of 20°C and -4.29V at 0°C. In case there is a
need of readjusting the voltage after servicing the LCD or exchanging
some of power source components, be sure to look on the LCD from
30° of angle from the vertical line while adjusting the pot.
:D.
mi-
Low side voltage of common signals (Hl-H7) for LCD.
High side voltage for segment signals (Sl - S40)
Intermediate voltage of the common and segment signals
Low side voltage of segment signals.
VA,
VM
and VB become pulses in an amplitude of several volts owing to influence
caused from the LSI.
VA:
VM:
VB:
NOTE:
ata
o The liquid crystal reference voltage VDISP is generated in the above circuitry in order to avoid
occurrence of such unpleasant phenomena as blurred character or contrast variation that might
degrade display performance, which is caused by a slight voltage variation in the liquid crystal
reference voltage VD ISP, since the 5
x
7 dot matrix liquid crystal is used in the display of this
pocket computer.
A) VDD is generated in the CPU II on the basis of VGG.
B) The gate voltage of MOS FET is controlled by the 250KS1 pot to regurate the voltage for VDISP.
Furthermore, the voltage of VDISP is changed by the thermistor to meet with temperature varia-
tion, so as to maintain proper display performance.
C) Line between the reference voltage VD ISP and GND is divided by resistor to make out VA,
VM
and VB.
VDISP:
20°
oo
C PUil
Yoo
Relation between ternperture and VDISP
MOS FET
ioo»
2-4. Power source