Tait T855 - Receiver

B5.18 T855 Fault Finding M850-00
31/09/98 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
Check VCO
frequency OK?
Readjust TCXO
frequency.
Check IF
alignment OK?
Adjust IF coils.
Fault find audio.
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
NY
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
Poor sensitivity:
worse than -117dBm.
A
Quad coil L390
tuned for min.
distortion (flat
audio response)?
Adjust L390.
Retune all
IF coils.
Check distortion
TP314 OK?
Inject on-channel
RF into mixer TP411.
Measure distortion.
OK?
Check distortion
TP314,
injecting 45MHz
@ -47dBm into TP310
at Q320 input. OK?
Inject 45MHz
after mixer IF
output TP412.
Measure distortion.
OK?
Fault in IC310,
&XF302, Q330,
Q320, &XF301 or
surrounding circuitry.
Check/replace.