User Manual

PINEAPPLE TECHNOLOGY, INC. VIII – ADJUSTMENTS AND TUNING
DTXPRO-1.2KU OPERATING AND SERVICE MANUAL
THE INFORMATION PROVIDED HEREIN IS PINEAPPLE TECHNOLOGY INCORPORATED PROPRIETARY INFORMATION
AND CANNOT BE COPIED OR DISTRIBUTED WITHOUT PRIOR AUTHORIZATION
VIII - 2
VIII --- ADJUSTMENTS AND TUNING
The DTXPRO-1.2KU is a new series of transmitters offered by Pineapple Technology, Inc. The
latest in LDMOS device and circuit technology are employed to ensure reliable and serviceable
operation for many years.
There are very few adjustments necessary to maintain full service condition. The following will
give the technician a general overview of locations for locating these adjustments:
1. MODULATOR - See details for all adjustments in the DXDPRO-10U Instruction Manual
provided on a CD with your transmitter. Should you have any questions, contact the
Pineapple Technology, Inc Engineering staff for assistance.
2. BPUD2.5K6S158-J - The ATSC digital mask filter provided with your transmitter has
been tuned at the factory and adjustments should not be necessary and are not
recommended. Any attempt to tune or modify this filter will void manufacturer's
warranty.
3. DX500A - This is the main PA board in the transmitter. Under normal operation, no
adjustments are necessary. In the unlikely event that a power transistor has to be
replaced, the bias adjustments should be reset to insure optimum operation of the
transmitter. The following procedure should be followed when making bias
adjustments:
a. Remove the PA1K-50 amplifier assembly from the transmitter and set it up on a
sturdy work bench. The bench should be equipped with a 50 VDC power supply
with current capacity of 10 Amps. A VOM will be required to measure the
voltage drop across the precision resistors located on the monitor board.
b. Attach 50 ohm load resistors to the input port and one to the output port. If this
is not done, severe damage to the PA is possible resulting in costly repair.
c. Connect the 50 VDC supply to the DC ± terminals. DO NOT TURN THE
POWER SUPPLY ON AT THIS TIME.
d. Locate the circuits where bias adjustments are necessary. Adjust only those
circuits where service was performed. Turn the bias adjustment POT's fully
counter clockwise You will find two (2) POT's for each power device with one on
each gate. These are small SMT components and require gentle handling.
e. Locate the current sense resistors on the monitor board. This is a 2 watt .01
ohm precision resistor. There is one for each device.
f. Turn the power supply on and measure the +DC to ensure that it reads +50
VDC.
g. Measure the voltage drop across the precision resistor. This should read zero
(0) VDC. Increase one of the bias POT's slowly till the meter reads 0.009 volts.
Increase the second POT until the reading is 0.018 volts. This completes the
adjustment.