Service Manual Part 1

  +8+
  
+8+8 3
Refer to the “Synthesiser Faults”, “Receiver Front End Faults” and “Receiver IF
Faults” fault finding charts in Section 5.10.
Check that the VCO is on the correct frequency, and that the receiver is correctly
aligned.
Check that the sensitivity into the front end is -119dBm (typical).
If the sensitivity is low (less than -117dBm), the fault can be traced by measuring
the sensitivity into successive circuit blocks. Prepare a test cable by connecting a
1nF capacitor to the end of a length of coaxial cable, as shown below.
 " ! 2) 3
 Before using the test cable, ensure the coax braid is connected to an earth point
on the PCB.
Using the RF test cable, apply a modulated signal to test points in the first IF sec-
tion, at the first IF frequency, as follows:
Alternatively, apply an on-channel RF signal to the front end test points.
Poor sensitivity indicates a fault in one of the circuit blocks following the test
point. For typical sensitivity levels, refer to the fault finding charts.
 Poor sensitivity at the mixer input can be caused by lack of drive level from the
VCO.
+8- 3)#9
Measure in-circuit RF levels with an RF probe. Typical RF levels can be found in
the “Transmitter RF Low Power Faults” fault finding chart, in Section 5.10.8.
 Shorten the RF probe earth lead to a minimum.
Model First IF Frequency (MHz)
T2000-100 27.7
T2000-200 10.7
T2000-300 27.7
T2000-400 27.7
2000-500 49.1
T2000-600 49.1
T2000-700/900 49.1
T2000-800 61.9
1nF
Coax
To Test Cable
Connect To Earth