Service Procedures; Service Note - Shure U2 Service Manual

Service Procedures

Service Note

Units With Date Codes
Earlier Than August 1996
25B1022 (AG)
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.
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Shure U2 Hand-Held UHF Transmitter
Service Procedures