Sharp ER-A57R1 Service Manual page 58

b) Connecting the oscillator and its adjustment
Connect a dummy network or branch-trunk network on to the output
of the ER-A6IN installed in the ER-A570, and connect the oscillator to
the dummy or branch-trunk network.
Fig. 4 Connection
∗ Waveform adjustment
Adjust VR1 until the signal waveform as shown in Fig. 5 is obtained
across TP (pin 1 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)
CPWBX7317RC01
Parts surface
GND PIN
MC68B54
Fig. 6 Board location
2 When the Branch Trunk Network and Two
ECR'S are Available.
a) Connecting terminals
Both ends of the network must be terminated with a 50Ω terminator. If
only two active terminals are to be tested and left on the network,
disconnect all other terminals from the network. (In this case as well,
both ends of the trunk network must be terminated with 50Ω).
R50 Ω
ER-A670/A650
Fig. 7 Terminal connection
b) Receive level adjustment
i) Turn on both the objective terminal of receive level adjustment
(receiver terminal) and the terminal which sends the adjusting
signal (transmitter terminal).
ii) Run the diagnostic program JOB#603 on the transmitter terminal
to send a flag.
R2
OSC
R1 C1
SRN connector
VOH
VOL
R3
TP
A
VR1 IRCCN
F1
R50 Ω
ER-A670/A650
Key operations: MODE switch: SRV position
601 TL
iii) Checking transmitter terminals' output waveform
Using an oscilloscope, check the transmitter terminal's output
signal waveform.
1µ S 1µ S
Fig. 8 Transmitter terminal's output waveform
At the receiver terminal, the transmitter terminal's output
waveform is subject to attenuation and distortion due to the length
of the trunk cable (this depends on the characteristics of the cable
itself).
Fig. 9 Example of distorted signal waveform at the receiver terminal
With the receiver terminal adjust VR1 (5kΩ) on the ER-A6IN board
until the waveform as shown in Fig. 10 is obtained at TP (pin 1 of the
75115). (For the location of VR1, see Fig. 6 Board location of this
subsection).
Clockwise rotation of VR1 extends the High level pulse width of the
signal at TP (pin 1 of the 75115).
1µ S 1µ S
Fig. 10 Waveform at TP (pin 1 of the 75115 IC in the receiver
5) Other Checks (These Checks should be
done After the Receive Level Adjustment
is Completed).
1 Line driver bias control circuit
Make sure that the voltage at the Α -side lead of the R3 resistor
(150Ω, 3W) shown in Fig. 6 is properly switched.
Procedure:
i) Connect a terminating resistor or read network to the BNC con-
nector, QCNW-6856RCZZ (Fig. 2).
ii) Run the diagnostic program JOB#604, and make sure that the
Α
voltage at point
4.3ms
17ms
Fig. 11 bias circuit switching waveform
Key operation:
602 TL
iii) If the waveform as shown in Fig. 15 is not obtained, it is most
probable that transistor Q3 (2SA509) is defective.
2
For the other check items, refer to III. TEST FUNCTION.
4 ™ 15
(at transmitter output)
(RG58/U 400m)
terminal)
(in Fig. 6) is switched as shown in Fig. 10.
3.8V
0.8V
12V
0V