Service Procedures; Service Notes; Product Changes - Shure U1 Service Manual

Service Procedures

Service Notes

Units With Date Codes
Earlier Than August 1996

Product Changes

25C1021 (BG)
Shure U1/U1L Body-Pack UHF Transmitter
A small number of synthesizer ICs (U204) can experience start-up
problems with the 4 MHz crystal reference oscillator. The problem will
only occur for certain values of tuning capacitance.
The transmitter displays the correct group and channel information.
However, the carrier will have moved to its lowest possible frequency
(around 750 MHz). The tuning voltage of the VCO will read 0 Vdc.
Adjusting the crystal's tuning capacitor to its lowest value should
cause the 4 MHz crystal oscillator to start up, and the carrier will lock
to the proper frequency.
The tuning capacitor can now be readjusted to center the carrier to
within ± 1000 kHz. However, once the unit is turned off, the problem may
return.
All units with August 1996 date codes or later have a 10 kΩ resistor
from pin 2 of the synthesizer to ground to insure that the internal
oscillator will start up for all values of tuning capacitance (C239). Safe
values for the resistor are from 16.8 to 33.2 kΩ.
Antenna Changes
All models shipped after February 1999 have a soldered attached
antenna (70A8017) to replace screw-on removable antenna.
Attenuator Switch SW201
Attenuator switch SW201 has been added to the audio section of the
rf-audio printed circuit board. All products shipped after February 1997
(board versions "F" and later) should include this switch.
Inductor L104 Removal
Inductor L104 has been removed for improved electrostatic
discharge (ESD) performance. On products shipped after March 1997,
L104 was replaced with a jumper.
On "F" and later versions of the board, the circuit was redesigned
and the jumper was removed. Shure recommends that any product
shipped before March 1997 have L104 removed and replaced with a
jumper.
Comparator U102
Comparator U102 has been changed to prevent an "88 88" display.
11 Service Procedures