May 25, 2005 6881096C74-B
4-24 Troubleshooting Procedures: 700–800 MHz Main Board Troubleshooting
3. Continue troubleshooting by using the Fail 001 troubleshooting chart in Chapter 5.
4.9.2 FGU Troubleshooting Aids
The following illustrations are additional service aids for troubleshooting the frequency generation
unit.
• Figure 4-10 on page 4-25 is a block diagram of the DC distribution for the frequency generation
unit.
• Figure 4-11 on page 4-26 is a block diagram of the frequency generation unit.
• Table 4-15 on page 4-26 describes the function of pins on the LV Frac-N IC U6751.
• Figure 4-12 on page 4-28 is a waveform representation during programming of the LV Frac-N
IC U6751.
Tx (TA) 851.0125 -
868.9875
F(U6754 osc2) =
Fc
851.0125 -
868.9875
Low HIgh Low Low
Tx (TA) = Talkaround Mode
Tx(RPTR) = Repeater or trunked
Table 4-14. VCO Frequency Calculation and Switching Logic (700–800 MHz) (Continued)
MODE
Radio
Frequency
(MHz)
VCO
Frequency
Formula
VCO
Frequency
(MHz)
AUX
1
AUX
2
AUX
3
AUX
4
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