Tait T850 II Series, Service Manual

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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 50
Ω
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 50
Ω
test break points have been included throughout the RF circuitry to enable
individual transistor stages to be tested.
Note 1: Use good quality 50
Ω
coax for the "flying" test leads.
Note 2: Ensure each output is terminated in a 50
Ω
load of the correct power rating.