Read Sharp ER-A750 (serv.man4) Service Manual online
CHAPTER 3. SERVICE PRECAUTION
1. Adjustment for SRN (IN-LINE) interface
circuit
If transistor Q10 in the transmitter/receiver section has been replaced
or if the SRN level requires readjustment, the following alignment is
required:
or if the SRN level requires readjustment, the following alignment is
required:
1) Tools and Instruments Required
1
Oscilloscope (50MHz or better) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2
ER-A750
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2) Dummy Network Specifications
Fig. 1 Dummy network
The oscillator should be connected to the points indicated by
⊕
and
$
.
⊕
: Connect the positive side of the oscillator.
$
: Connect the negative side of the oscillator.
3) Connections
Fig. 2
Attach the BNC connector to the SRN connector (CON 15) on the
main PWB.
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.
Fig. 3 1MHz oscillator output waveform
NOTE: The oscillator used should have an output impedance of
50
Ω
.
b) Connecting the oscillator and its adjustment
Connect a dummy network or branch-trunk network to the output of
the SRN connector (CON 15), and connect the oscillator to the
dummy or branch-trunk network.
the SRN connector (CON 15), and connect the oscillator to the
dummy or branch-trunk network.
*
Waveform adjustment
Adjust VR4 until the signal waveform as shown in Fig. 5 is obtained
across IC34 (pin 1 of the 75115) and GND pin.
Turning VR4 clockwise extends the interval of T1.
across IC34 (pin 1 of the 75115) and GND pin.
Turning VR4 clockwise extends the interval of T1.
Fig. 5 Receiver regeneration waveform (with dummy network)
Fig. 6 Board location
2
When the Branch Trunk Network and Two POS’S are
Available.
Available.
a) Connecting terminals
Both ends of the network must be terminated with a 50
Ω
terminator. If
only two active terminals are tested and left on the network, discon-
nect all other terminals from the network. (In this case as well, both
ends of the trunk network must be terminated with 50
nect all other terminals from the network. (In this case as well, both
ends of the trunk network must be terminated with 50
Ω
).
Fig. 7 Terminal connection
R1 100
Ω
J (1/4W carbon)
R2 150
Ω
J (1/4W carbon)
C1 0.01µ F (mylar firm)
C1
R1
R2
BNC connector
Main PWB
5V
0V
0.5µ S
0.5µ S
VOH
VOL
T1 = 580 to 620ms
T2 = 380 to 420ms
T2 = 380 to 420ms
T1
T2
Main PWB
VR
4
IC
3
4
Q10
Pi
n
N
o
.1
R4
CO
N15
A
ER-A750
R50
Ω
R50
Ω
ER-A750
3 – 1
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