Harris DX 25U, Техническое руководство

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These boards are:
•
Analog to Digital Converter (A34)
•
Analog Input Board (A35)
•
Oscillator (A17)
•
Driver Supply Regulator (A22)
•
DC Regulator (A30)
•
Output Monitor (A27)
•
LED Board (A32)
•
Driver Encoder/Temp Sense Board (A19)
•
Switch Board/Meter Panel (A31)
5.6.1
Analog to Digital Converter (A34)
The Analog to Digital Converter contains two adjustments, two
DIP switches, and two sets of jumpers. The first step in replacing
the Analog to Digital Converter is to make sure that switches S1
and S2 are set the same as the board to be replaced. S1 sets the
A/D sample phasing and is critical to the proper operation of the
transmitter. Set jumper P10 and P11A/B to the same settings as
on the board to be replaced.
5.6.1.1 Delay Adjustment: R78
The delay adjustment is normally set during factory testing of
the board but can be checked and adjusted if needed using the
following procedure:
a. Once the new Analog to Digital Converter is installed,
apply low voltage to the transmitter and verify that all
LED’s on the ColorStat™ panel are green.
b. Locate the PA TURN-Off switch S2 on the Controller and
move it to the OFF (up) position.
c. Depress the LOW power button on the front panel and note
that the transmitter completes the step-start sequence and
that the +230 Vdc supply energizes.
d. The PA OFF indicator LED of DS1 on the Modulation
Encoders (A37) should be illuminated and there should be
no rf output.
e. Connect a scope with a minimum bandwidth of 30
MHz to TP3 on the Analog to Digital Converter and
ground the probe on TP19, 20, or 21. This is the
conversion pulse for the A/D converter IC. The width
of the positive portion of the pulse should be approxi-
mately 40ns.
f. Adjust the pulse to the correct width with R78. The Con-
version Error LED DS1 on the Analog to Digital Converter
should be green.
5.6.1.2
Offset Adjustment: R7
The Offset adjustment is set during factory testing of the board,
but can be adjusted if needed. The most significant affect of the
offset adjustment is on modulation tracking. In other words,
equal modulation percentage at all power levels. To check the
setting of the Offset adjustment:
a. Operate the transmitter at 25 kW and modulate with a
100Hz tone at 95%.
b. Operate the transmitter at 5.0 kW and measure the percent of
modulation. If it is within 1% of the level noted at 25 kW, no
further adjustment of the Offset control is necessary.
c. If the modulation is not within 1% of the level noted at 25
kW, adjust R7 to bring the modulation level within 1%.
d. Operate the transmitter at 25 kW and note the percent of
modulation. Adjust R7 if necessary.
This adjustment will affect the power output on all power set-
tings, but will have the most affect at low power. Normally,
satisfactory modulation tracking should be obtained within two
turns of where the control was previously set.
5.6.2
Analog Input Board (A35)
The Analog Input Board has five adjustments that are preset
during factory tests. It is normally advisable to recheck these
settings using the procedures given here, however it may be
necessary to install the board quickly to return the transmitter
to the air. In this case, the adjustments can be set to the same
resistance values as on the board to be replaced and a complete
set-up procedure can be performed later. This procedure as-
sumes the controls on the board to be replaced have not been
changed from their factory settings. The controls to be preset,
and the most convenient measurement points given are shown
in Table 5-1.
5.6.2.1
Dither Frequency Adjust: R41
Dither Frequency adjustment is factory set and should not need
any further adjustment. To check the dither frequency:
a. Connect a frequency counter to TP10.
b. Adjust R41 for a nominal frequency of 72 kHz. This is not
critical and can vary anywhere from 70 kHz to 74 kHz.
5.6.2.2 Maximum Power Adjust: R27
a. Turn on the transmitter at LOW power with no modulation.
If the Maximum Power adjust is set correctly the transmit-
ter should come up at the previously set low power level.
b. If it does not, adjust R27 for the correct low power output.
CONTROL FUNCTION MEASUREMENT POINTS RECORDED VALUE
R15 AUDIO GAIN ADJ. U6-2 to R16 (Left side)
R27 MAX. POWER ADJ. TP3 to ground
R41 DITHER FREQ ADJ. U3-2 to junction of R38, R39, CR11
R43 DITHER LEVEL ADJ. TP9 to ground
R84 OFFSET ADJ. R83 (right side) to ground
R85 GAIN ADJ. U5-5 to ground
Table 5-1. Analog Input Board A35 Preset Controls
DX-25U
5-6 888-2297-002 Rev. Z1: 06-02-00 Additional info to ECN 46105
WARNING: Disconnect primary power prior to servicing.