Motorola HT-1000 Service Manual page 48

TX VCO Crossover
Procedure
26
Since the transmit crossover frequency has changed, whenever
transmit VCO crossover alignment (an RSS function) is performed,
UHF band split and circuit board identification will be important.
• UHF band split can positively be determined by the markings on
the power amplifier shield. If the power amplifier shield marking
is 25U04 or 85Y10, then the transceiver is a 403 - 470MHz band
split. If the power amplifier shield marking is 25U05 or 85Y11,
then the transceiver is a 450 - 520MHz band split.
• The "C" kits can be identified by the circuit board number
4221J07 or 4221J37 visible on side 2 of the board, located along
the circuit board edge just next to crystal filter FL1. All future UHF
transceiver boards will be in the "4221J" series.
Anytime a controller board or transceiver board is replaced in a radio,
it will be necessary to perform the RSS transmit VCO crossover
alignment, and check the transmit VCO crossover frequency. The RSS
screen for this alignment will show a "current value" box
with a frequency already assigned, placed inside the box. When
performing transmit VCO crossover alignment, determine the UHF
transceiver band split, and then check the transceiver circuit board
number. In a UHF radio (450 - 520MHz range):
• If the board number is any "4221J" series number, other than
4221J01 thru 4221J06 or 4221J36, the transmit VCO crossover
frequency in the "current value" box should be 495.375MHz. If it
is not, change it to 495.375MHz.
• If the board number is 5521Y03, the transmit VCO crossover
frequency in the "current value" box should be 486.025MHz. If it
is not, change it to 486.025MHz.
VCO varactors (CR201, 203, 207, 208, and 209) in "C" and later kits
are not interchangeable with VCO varactors in earlier kits; Motorola
parts and part numbers are different. When replacing a VCO varactor,
identify the UHF transceiver band split and the transceiver circuit
board number, and then order replacement parts from the applicable
parts list.
1. From the SERVICE menu, press F2 to select TRANSMITTER
alignment.
2. Press F7 to select the TRANSMIT VCO CROSSOVER softpot. The
screen will indicate the transmit test frequency to be used.
3. Connect a dc voltmeter capable of 1mV resolution to test point 5
(TP5), which is accessible through a hole in the bottom side VCO
circuitry shield.
4. Beginning with the default softpot frequency of line 2, press F6 to
key the transmitter, and adjust the UP/DOWN arrow keys until the
voltage reading at TP5 is 3.0 ±0.1 volts. The frequency will
increment in steps of 50kHz.
5. Press F6 again to dekey the transmitter, and press F8 to program
the softpot value.
6. Press F10 twice to return to the SERVICE menu.