SG-2000 MANUAL
184
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if it were a receive signal. The speaker is enabled by holding SPE low in CW
mode.
The receive audio signal is digitized for use by the squelch by over driving
IC12A. The output on pin 7 of IC12A is a clipped version of the receive audio
signal. This is inverted by IC13A which is the TMR signal. The TMR signal has a
pulse repetition rate equal to the receive audio frequency.
23.3.3.
Test Setup
Visual inspection. Look for any quality defects.
Check all diodes and electrolytic capacitors for polarity.
Check for solder bridges and shorts. Compare to the sample display board.
Use the multimeter in the Ohms position. Check for short circuits on the VREF,
5VG, 5V, 8VG, 13.6VSW and OVEN lines.
Connect SG-2000 remote head cable from J503 on the SG-2000 to J1 on the
display board under test.
Connect extender cable from J1 on the Test Head Microprocessor Board With
Display Test Chip to J2 on the display board under test.
Connect keyboard extender cable from J1 on the Test Head board to J3 on the
display board under test. (At this stage there is no LCD installed on the PCB).
Connect the RF output of the SG-2000 to a power meter and then to a 50?
dummy load.
LCD Installation
Turn on the power supply. After the standby LED comes on, apply power to
the display by pressing the "POWER" button on the head.
Test for the following voltages.
5 VDC on each side of R13
5 Vpp clock of 65 Hz on each side of R12
Turn the power off.
Install new LCD, lamps and foam. See the working sample of Display PCB on
the Display PCB under test.