Table 4-7. Test Mode Channels Uhf Range 1 (Aux 4 Is Not Used For Vco Selection In Uhf); Table 4-8. Vco Frequency Calculation And Switching Logic (Uhf Range 1) - Motorola ASTRO XTL 1500 Detailed Service Manual

4-12 Troubleshooting Procedures: UHF Range 1 (380–470 MHz) Band Main Board Troubleshooting

Table 4-7. Test Mode Channels UHF Range 1 (AUX 4 is not used for VCO selection in UHF)

AUX (TX Logic)
Test
Mode
1 2
0 0
Chan 1
Chan 2 0 0
Chan 3 0 0
Chan 4 0 0
1 0
Chan 5
Chan 6 1 0
Chan 7 1 0
1 0
Chan 8
NOTE: The UHF band radios use high-side injection with an IF frequency of 109.65 MHz; therefore,
the receive VCO frequencies are 109.65 MHz higher than the selected radio channel
frequencies.

Table 4-8. VCO Frequency Calculation and Switching Logic (UHF Range 1)

VCO
RX VCO Q5901
RX VCO Q5903
RX VCO Q5905
TX VCO Q5825
TX VCO Q5826
NOTE: If a failure is indicated in any of the VCOs, whose operation is defined in the table above, then
the respective circuit should be checked to ensure proper bias is being applied to the
transistor. Specifically, the transistor collector pin should be at 8.2 V and base-emitter voltage
should be on the order of 0.8 V. The steering line voltage should be in the range of 2 V for the
lower frequency end of operation, and on the order of 11V at the upper frequency end of
operation. There could be typically +/- 1 V deviation from the above quoted numbers, which
allow for tolerances in the components. A clean, steady, frequency spike should be observed
on a spectrum analyzer of typically -18 dBm at the end of the resistive pad in the collector
circuitry of a properly working VCO.
3. Continue troubleshooting by using the Fail 001 troubleshooting chart in Chapter 5.
June 15, 2005
TX TX Freq
VCO
(MHz)
3
0
Q5825 380.0250
0 Q5825 391.4750
0 Q5825 408.9750
0 Q5825 424.9375
0
Q5826 425.0250
0 Q5826 436.0250
0 Q5826 455.8750
0
Q5826 469.9375
AUX1 AUX2
0 1
1 1
0 0
0 0
1 0
AUX (RX Logic)
RX
VCO
1 2 3
0 1 0 Q5901
0 1 0 Q5901
0 1 0 Q5901
1 1 0 Q5903
1 1 0 Q5903
1 1 0 Q5903
0 0 1 Q5905
0 0 1 Q5905
AUX3 VCO Frequency
0
489.65 <= f < 519.65
0 519.65 <= f < 549.65
1 549.65 <= f < 579.65
0 380 <= f < 425
0
425 <= f <= 470
RX VCO
RX Freq
Freq
(MHz)
(MHz)
380.0750 489.7250
391.4250 501.0750
408.9250 518.5750
424.9875 534.6375
425.0750 534.7250
436.0750 545.7250
455.8250 565.4750
469.9875 579.5750
6815854H01-A