B5.18
T865 Fault Finding
M860-00-Preliminary
30/06/98
Copyright TEL
5.7.6
Receiver
Refer to the receiver IF and front end circuit diagrams (sheets 3 & 4) in Section 6.
High audio
distortion.
B
Note: T.B. = Test Break
(refer circuit diagrams)
Quad coil L360
tuned for min.
distortion (flat
audio response)?
Adjust L360.
Retune all
IF coils.
Check VCO
frequency OK?
Readjust TCXO
frequency.
Check IF
alignment OK?
Adjust IF coils.
Check distortion
IC350 pin 7 OK?
Fault find audio.
Check distortion
IC350 pin 7,
injecting 21.4MHz
@ -47dBm into T.B.
at &XF330 input. OK?
Fault in IC350,
&XF340, IC340,
&XF330 or
surrounding circuitry.
Check/replace.
Inject 21.4MHz
after mixer IF
output T.B.
Measure distortion.
OK?
Inject on-channel
RF into mixer T.B.
Measure distortion.
OK?
OK
Check
sensitivity
into each
IF stage.
Repair stage.
Replace TCXO.
Refer to
synthesiser
fault finding
charts.
Check TCXO
stability OK?
(see 5.5.3)
N
Y
N
Y
N
Y
N
Y
N
Y
N
Y
N
Y
Y
Y
Ensure VCO, RF
front end & IF
correctly aligned.
High audio
distortion?
Check/repair faulty
stage or component.
Check DC
conditions OK?
(see cct diagrams)
Check sensitivity
into each stage
(see 5.5.2)
See Chart B
(below).
Replace
faulty device.
Y
N
N
Y
Ensure links SL405
to SL440 & link B
are set correctly.
(see Section 3.7)
Poor sensitivity:
worse than -117dBm.
A
Содержание T860 Series II
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