Kenwood NX-3400 Service Manual page 67

[Inspection procedure]
● Unlock [Unlock beep / VCO assist tuning is impossible] *Include modulation problems
Assist Auto Tuning
↓
Auto tuning NG
↓
↓
Assist Manual Tuning
↓
Manual tuning NG
↓
↓
○ Check the VCO output signal
Observe the signal at point A with spectrum analyzer thru high impedance probe
↓ ↓
Signal existence
No signal
↓ ↓
↓ Remove <R198> and check whether it is short circuited at point A
↓ ↓
No short-circuit
↓ ↓
↓ ↓
↓ ↓
↓ ○Check the VCO power supply
↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓ ■There is a problem with the VCO circuit inside a BLS / Please replace to new PCB
↓
↓
○ Check the VCO Assist voltage supply circuit
Remove <C118> and measure the voltage at point D by setting Assist tuning value [4096]
↓
This voltage fluctuatein conjunction
↓
with the change of Assist tuning value
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
Observe the signal at point A with spectrum analyzer thru high impedance probe
↓
This signal fluctuate in conjunction
↓
with the change of the voltage at point E
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
○ Check the VCO control voltage supply circuit
↓
↓
↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓ ↓
↓ ■There is a problem with the VCO circuit inside a BLS / Please replace to new PCB
↓
Please refer to [Remarks] below.
[Remarks]
The following things are assumed as causes of trouble besides the above
• PLL data is abnormal
• VCO/PLL lock judgment is abnormal[<IC401>MPU/DSP IC]
■There is a problem with the VCO circuit inside a BLS / Please replace to new PCB
*In case, Radio frequency is set under 870MHz
Measure the voltage at point B or C
In case, other than those above
The checked voltage is ↓ The checked voltage is about 4.2V.
not about 4.2V. ↓
■There is a problem with the VCO circuit inside a BLS / Please replace to new PCB
Remove <R116> or <R117> and measure the voltage at point B or C
The checked voltage is ↓
The checked voltage is to greatly differ from 4.2V.
about 4.2V. ↓
□There is a problem outside the BLS. Check the power supply circuit.
↓
The checked voltage is about 0V. *Modulation problems may occur if this point[D] be abnormally condition.
↓
Remove <R108><R109> and measure the voltage at point E
↓
This voltage fluctuatein conjunction
↓
with the change of Assist tuning value
↓
↓ *In case of tuning value is [1] , this voltage is about 0V
↓ In case of tuning value is [4096] , this voltage is about 15V
↓
■There is a problem with the VCO circuit inside a BLS / Please replace to new PCB
Measure the voltage at point F
* In case of Assist tuning value is [1] , this voltage is about 4.7V
In case of Assist tuning value is [4096] , this voltage is about 0.1V
This voltage fluctuatein conjunction
with the change of Assist tuning value
Remove <IC102> and measure the voltage at point G
This voltage difference between
point F and point G is more than 0.1V
↓
Short-circuit
↓
point B
point C
*In case, Radio frequency is set under 870MHz
In case, other than those above
*When measuring this point, please use a multimeter with sufficiently high input impedance
↓ The checked voltage is about 0V.
↓
□There is a problem outside the BLS. Check the Assist voltage supply circuit.
↓
This signal doesn't fluctuate in conjunction
↓
with the change of the voltage at point E
↓
↓
■There is a problem with the VCO circuit inside a BLS / Please replace to new PCB
↓
When the above condition is not satisfied
↓
↓
□There is a problem outside the BLS. Check the circuit around IC303.
↓
This voltage difference between
↓
point F and point G is less than 0.1V
↓
□There is a problem outside the BLS. Please check the circuit posterior to <IC102>
point B
point C
*Assist voltage switch<Q102> is on in the state of Assist tuning mode
(No.RA070<Rev.001>)1-67