Sharp UP-3300 Service Manual page 15

CHAPTER 3. SERVICE PRECAUTION
1. Adjustment for SRN (IN-LINE) interface
circuit
If transistor Q6 in the transmitter/receiver section has been replaced
or if the SRN level requires readjustment, the following alignment is
required:
1) Tools and Instruments Required
1
Oscilloscope (50MHz or better). . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2
UP-3300 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2) Dummy Network Specifications
R1 100 Ω J (1/4W carbon)
R2 150 Ω J (1/4W carbon)
C1 0.01µ F (mylar firm)
Fig. 1 Dummy network
The oscillator should be connected to the points indicated by
.
$
⊕
: Connect the positive side of the oscillator.
$
: Connect the negative side of the oscillator.
3) Connections
Main PWB
Attach the BNC connector to the SRN connector (CN2) on the main
PWB.
4) Alignment Procedure
1 When Using an Oscillator
a) Checking the 1MHz oscillator output
Using an oscilloscope check the 1MHz oscillator's output waveform.
5V
0V
0.5µ S 0.5µ S
Fig. 3 1MHz oscillator output waveform
NOTE: The oscillator used should have an output impedance of
50Ω.
b) Connecting the oscillator and its adjustment
Connect a dummy network or branch-trunk network to the output of
the SRN connector (CN2), and connect the oscillator to the dummy or
branch-trunk network.
R2
R1
C1
⊕
BNC connector
Fig. 2
* Waveform adjustment
Adjust VR1 until the signal waveform as shown in Fig. 5 is ob-
tained across IC5 (pin 15 of the 75115) and GND pin.
Turning VR1 clockwise extends the interval of T1.
T1 T2
T1 = 580 to 620ms
T2 = 380 to 420ms
Fig. 5 Receiver regeneration waveform (with dummy network)
and
2. Calibration
1. Calibration
The coordinates on the touch panel and those on the VGA display
may not match for the following reasons.
•
The physical deviation between the touch panel and display
•
Variations in "electric resistance>coordinate" conversion on the
touch panel
Correction of such a deviation is called calibration.
2. Timing of starting calibration
Calibration is started at the following two cases:
– SRV reset/MRS –
1) When touch panel is pressed:
Calibration is started when PROGRAM reset/MRS is performed
with the touch panel pressed.
2) When no calibration has been performed:
Calibration is started when the calibration data held by the touch
panel controller is broken.
But case 2 isn't performed if case 1 is performed prior to the
second.
Calibration is also started when the EEPROM on the touch panel
PWB is replaced.
NOTE: If the touch panel unit is replaced for any reason such as a
repair, start calibration, following case 1).
3. Calibration specifications
1) The character string "Calibration Mode" is displayed.
2) If the touch is kept pressed, the machine waits for the finger
leaving the touch panel.
3) The character string "Touch these crosses" is displayed.
4) Entering correction mode
The command "Entering correction mode" is issued to the touch
panel controller.
At this step, the coordinate data of the four corners in the input
area are passed to the controller.
3 – 1
CN2
VR1
IC5
Pin No.15
R2
Fig. 6 Board location
VOH
VOL
A