Shure UHF MD Manuel de service télécharger pdf (Page 12)

Shure U2 Hand-Held UHF Transmitter

Service Procedures25B1022 (AG) 11

Service Procedures

Service Note

Units With Date Codes

Earlier Than August 1996

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 UHF MD Manuel de service Page 12