User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 48
Original 11/97
• Check the tune voltage at pin C. It should fall in the range of 1.5 to 3.5 V.
If not, check the PLL IC. Ensure that the RF feedback is correct into the PLL at pin 6.
• The RX_LO gain stage N704, pin 3 should be about 3.40 V.
If not, check R803 and see that VRX is 4.40 V at C206.
• The TX_LO gain stage N705, pin 3 should be about 2.70 V
If not, check R809 and R815. Ensure that VTXT is approximately 4.40 V at R809 or
C212.
Chart of Synth DC Node Voltages – AMPS Troubleshooting Mode
Node Voltage
(approx)
(V)
G300 – VCTCXO bias, pin4
3.60
G300 – VCTCXO Tune voltage, pin 1
1.50 – 3.50
N301 – PLL IC bias, pins 4, 5
3.15
N301 – PLL IC bias, pin 18
4.15
N301 – PLL IC bias, pin 19
2.80
V301 – Varactor diode – 180 MHz tune voltage
1.50 – 3.50
V303 – VHF Buffer Amp – Collector
4.30
V303 – VHF Buffer Amp – Base
3.30
V303 – VHF Buffer Amp – Emitter
2.60
V302 – VHF Oscillator – Collector
2.60
V302 – VHF Oscillator – Base
2.30
V302 – VHF Oscillator – Emitter
1.73
G301 – UHF VCO bias, pin B
4.00
N704 – UHF RX_LO gain stage
3.40
N705 – UHF TX_LO gain stage
2.70
RF Node Power Levels
A high impedance passive RF probe may be used with a spectrum
analyzer to obtain the RF nodal power levels for the synthesizer circuit.
The following levels assume the above probe. The phone was also
operating in the AMPS Troubleshooting Mode via Service Software. The
blank column is reserved for values the user will obtain with his or her own
probe.