Incorrect Values At U602, Pin 19 - Motorola ASTRO Digital Spectra Plus Service Manual

4-6
5. Check the positive steering line, J601, pin 1 or 2 for positive voltage between 1.0 and 8.0 V. If
not correct, go to "Incorrect Voltage at Positive Steering Line"; otherwise, continue with the
following checks.
NOTE: It is common for both steps 3 and 5 to be incorrect in an "out-of-lock" condition.
6. Check U602, pin 27 for a 1.5 Vp-p square wave whose frequency is determined in the
following equation. If the values are not correct, go to "Incorrect Values at U602, pin 27."
Freq into U601-1 / Prescaler Modulus;
for example, F
F / (P+1) = 455 MHz / 256 = 1.76 MHz.
in
NOTE: The frequency at U601, pin 40, is seldom exactly equal to "F

4.1.4.1.1 Incorrect Values at U602, Pin 19

1. If the reference frequency is not equal to 6.25 kHz (800/900 MHz) or 5.0 kHz (VHF/UHF),
check U602-7 for 300 kHz, 0- to 9-V square wave. Then:
a. If 300 kHz is good, check the power to U602, pins 30 and 37. Also, check the serial data
programming by pressing and holding the mode select button and probing pins 11, 12,
and 13. The 0- to 5-V logic waveforms should appear similar to the following:
NOTE: The above waveforms are crude representations.
b. If the programming appears normal and the power supplies have all checked out correctly,
the out-of-lock condition is caused by a defective synthesizer IC (U602).
2. If 300 kHz is not present, check U602, pin 16, for 2.1 MHz, 1.5 Vp-p square wave.
a. If the signal is present and the power to the chip is normal, the condition is caused by a
defective synthesizer IC (U602).
b. If the signal is not present, check for the same signal at U601, pin 18. If not on pin 18,
check the reference oscillator output signal at U601, pin 21; it should be 16.8 MHz,
300 mVp-p. If the reference oscillator signal is present and the prescaler power supply
voltages are normal, the prescaler IC(U601)is defective.
c. If the reference oscillator signal (16.8 MHz) is not present on U601, pin 21, check U600,
pin 1 for 3.25 Vdc, pin 2 for ground, pin 3 for 16.8 MHz at 300 mVp-p, and pin 4 for
5 Vdc.
NOTE: Before concluding that the reference oscillator is defective, remove it from the
October 28, 2002
/ P = 455 MHz / 255 = 1.77 MHz, or
in
1" because the prescaler is continuously changing from one division to the other. In
the above example, P is 255 and P+ 1 is 256.
PIN 13 (Chip Select)
PIN 12 (Data)
PIN 11 (Clock)
board, power it up externally, and test it as an independent circuit.
Troubleshooting Procedures: ASTRO Spectra Procedures
" divided by "P" or "P+
in
6881076C25-D