Tait TM8100 mobiles, Service Manual

Page: 247 / 620

TM8100/TM8200 Service Manual Receiver Fault Finding 247
© Tait Electronics Limited November 2007
10 Receiver Fault Finding
Fault Conditions
This section covers the diagnosis of faults in the receiver. The fault-diagnosis
procedures consist of 18 tasks grouped into the following sections.
The symptoms of the fault in the receiver circuitry determine which
sections are relevant:
■
Faulty Receiver Sensitivity
■
Excessive Loss of Sensitivity
■
Moderate or Slight Loss of Sensitivity
■
Incorrect RSSI Readings
■
Faulty Radio Mute
■
High Receiver Distortion
If the receiver sensitivity is low, begin with “Faulty Receiver Sensitivity” on
page 248 to determine the extent of the loss in sensitivity.
CCTM Commands The CCTM commands required are listed in Table 10.1 . Full details of the
commands are given in “Computer-Controlled Test Mode (CCTM)” on
page 123 .
Frequency Bands
Where test procedures or figures differ according to the frequency band of
the radio, the frequency band is given in brackets. The frequency band may
be referred to as either ‘VHF’ (very high frequency) or ‘UHF’ (ultra high
frequency) or identified by the frequency sub-band, such as ‘B1’ or ‘H7’.
The product-code label on the radio body will identify the frequency band
as described in
“Product Codes” on page 17 . A definition of frequency
bands is given in “Defining Frequency Bands” on page 131 .
Table 10.1 CCTM commands required for the diagnosis of faults in the receiver
Command Description
72 Read lock status of RF PLL, FCL and LO2 — displays xyz (0=not in lock, 1=in lock)
101 x y 0 Set transmit frequency ( x in hertz) and receive frequency ( y in hertz) to specified values
376 Read tuning voltage for front-end circuitry — displays voltage x in millivolts
378 Read signal power at output of channel filter — displays power x (square of amplitude