QUANTUN QP650U Plus, Service Manual

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QP-650U Plus Circuit Description
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Circuit Description
1. Power Supply
Power supply of the radio is derived from the battery, which supplies battery B+ through power
switch. U608 supplies 5V (5M) voltage for the control circuit. U607 supplies 3V voltage for the PLL circuit.
And U200 supplies voltage for the transmit(V_TX), receive(V_RX) and vco(V_SAVE) circuit.
Fig. 1 Power Supply Block Diagram
2
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PLL frequency synthesizer
PLL circuit generates the first local oscillator signal for reception and RF signal for transmission.
Fig.2 PLL Block Diagram
PLL circuit
Step frequency of PLL can be 2.5 KHz, 5.0 KHz or 6.25 KHz. A 12.8MHz reference oscillator signal
is divided at U610 by a counter to generate a 2.5 KHz, 5.0 KHz or 6.25 KHz reference frequency. Output
signal from VCO is buffer amplified by Q103 and divided at U610 by a frequency divider. The divided
signal is compared with 2.5 KHz, 5.0 KHz or 6.25 KHz reference signal in the phase comparator of U610.