Cobra MR HH475 FLT BT, Руководство по обслуживанию

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TROUBLESHOOTING
Item Symptom Possible Cause
1 Unit does not turn on.
Defective power switch VR3.
Check the battery voltage.
Defective regulator U8.
2
Speaker no sound with
AF signal applied to
volume control
Defective volume control.
Defective speaker.
Defective U11 and/or associated components.
3 Squelch circuit inoperative
Check squelch control.
Defective U1 and/or associated circuitry between pin 9, 10 and
11.
4 No receive (RX)
Defective regulator U8.
Check TP1 voltage 0.5 – 4V;
Check second OSC 20.95MHz, pin9 of U6;
Defective Q7, Q8, Q2.
Check U1 audio output voltage at pin 9.
Defective F1 and F2;
5 Low receiver sensitivity
Check antenna and connector for possible corrosion or bad
connection.
Failure of the output from Q7, Q8, Q2, U1
Check the output level of local OSC.
6 No transmit (TX)
Defective PTT switch.
Defective regulator U8.
Check TP1 voltage 0.5 – 4V;
Check power transmits circuit Q12, Q6, D1, D2 and Q1;
Check power control circuit Q17, Q18, Q24;
Check power control circuit U2;
7 Low RF power output
Check RF power output from Q6, If it checks good, then check
and antenna switching diode D1, D2.
If not good then check the voltage level outputs of the drive
amplifiers Q3 and Q12 as well as the associated circuitry.
8 Poor or no modulation
Defective microphone.
Defective U4 and/or its associated components.
9
Deviation of transmit
frequency
Check crystal X2 and VC1.
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