Troubleshooting - Cobra MR HH325VP Service Manual

Item Symptom
1 Unit does not turn on.
Speaker no sound with
2 AF signal applied to
volume control
3 Squelch circuit inoperative
4 No receive (RX)
5 Low receiver sensitivity
6 No transmit (TX)
7 Low RF power output
8 Poor or no modulation
Deviation of transmit
9
frequency
TROUBLE SHOOTING
Possible Cause
Defective power switch VR3.
Check the battery voltage.
Defective regulator U8.
Defective volume control.
Defective speaker.
Defective U11 and/or associated components.
Check squelch control.
Defective U1 and/or associated circuitry between pin 9, 10 and 11.
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;
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.
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;
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.
Defective microphone.
Defective U4 and/or its associated components.
Check crystal X2and VC1.
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