User Guide

PAMS
Technical Documentation
NHD–4
Disassembly & Troubleshooting
Page 49
Original 11/97
Node Frequency
(MHz)
Power Lvl
HP10020A
500 ohm tip
(dBm)
Power Lvl
(your own)
(dBm)
G300 – VCTCXO, pin 1
15.36 –15.0
V303 – VHF Buffer Amp – Collector
180 –24.0
V303 – VHF Buffer Amp – Emitter
180 –30.0
V302 – VHF Oscillator – Collector
180 –30.0
G301 – UHF VCO, pin P
926.52 –30.0
N704 – UHF RX_LO gain stage
926.52 –20.0
N705 – UHF TX_LO gain stage
926.52 –40.0
Hints and Suggestions
• If no spectrum analyzer is available, a lot can be learned about the
health of a PLL by checking the control voltage tuning the VCO. If the
PLL is locked, this control, or tune voltage will fall between 1.5 and 3.5 V
DC. If the control voltage is near 0.0 or 4.4 V, the loop is most likely
unlocked.
• Probing the cathode of the varactor diode, V301 may unlock the VHF
loop.
•Modulation cannot be seen on the anode of the varactor when using an
oscilloscope. The level is two low. Instead, measure it at R317/C341
node.
• To check to see that the PLL IC (N300) is programmed by the CDSB
ASIC (D704), probe the CLK, DATA and RX_LE lines with an oscilloscope.
Monitor the oscilloscope when the channel is changed. Use the Service
Software test functions to change the channel. When the channel is
changed the PLL IC is reprogrammed. The RX_LE line will provide 5
evenly spaced pulses. The CLK signal will be a square wave, 0.0 to 3.0 V,
and the DATA line will show a stream of pulses, with no discernible
pattern.
• To check the functionality of a VCO, apply an external DC supply to the
control voltage pin, like the C pin of G301. The output frequency of the
VCO will change when the control voltage is varied.
AGC Troubleshooting
Introduction
Detailed below are a number of tests designed to demonstrate the
functionality of the features and systems described above in the
Functional Description. All make use of the control abilities of the Service
Software, all located in the Testing menu of the software package. AMPS
feature testing is mainly performed from the AMPS/Baseband test suite.
CDMA feature testing makes use of a menu of CDMA system controls.
The two most useful features of the later group are the CDMA TX Manual
Gain controls and the CDMA RX Manual Gain controls. The PDM controls
are also used extensively throughout the testing procedures.