HYT TM-800K, Service Manual

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TM-800K Service Manual
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The outputted signal is amplified by Q703, Q124, and then divided by PLL IC into 2.5KHz, 5KHz or
6.25KHz signal. The divided signal is compared with 2.5KHz, 5KHz or 6.25KHz reference signal from
16.8MHz crystal oscillator (2.5 PPM frequency stability) in the phase comparator. The frequency control
voltage outputted from the phase comparator is sent to TX VCO after passing through LPF (Q804,
Q805). In the meantime, modulation signal (TX) is passed to TX VCO for frequency modulation.
The working principle in receive mode is similar to that in transmit mode.
Figure 3 PLL Circuit
Control Circuit
Circuit in this section is comprised of CPU, reset IC, power supply controller and flash ROM.
CPU
IC120 (CPU) operates at 9.8304MHz. It controls the data transmission between receive circuit,
transmit circuit, control circuit, display circuit and peripheral circuit.
Figure 4 Control Circuit