D4.4
T858/859 Fault Finding
M850-00
31/09/98 Copyright TEL
4.4 RF Checks
4.4.1 General
You can measure in-circuit RF levels around Q1 and Q3 with an RF probe on which the
earth lead has been shortened to a minimum (i.e. 13mm); refer to the PA Fault Finding
Charts (Section 4.6.1 or Section 4.6.3 as appropriate). You must measure all other stages
with a power meter at the 50Ω points in the circuit.
For problems with the power control circuitry, refer to the Power Control Fault Finding
Charts (Section 4.6.2 or Section 4.6.4 as appropriate).
4.4.2 PA Faults
If a PA fault has occurred, or is suspected, it is easier to find if the various stages are iso-
lated by use of the test breaks (refer to Figure 4.1) and each stage analysed individually.
These 50Ω test break points have been included throughout the RF circuitry to enable
individual transistor stages to be tested.
Note 1:
Use good quality 50Ω coax for the "flying" test leads.
Note 2:
Ensure each output is terminated in a 50Ω load of the correct power rating.
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