Diagnosis Method Of Failure Around Pwb - Sharp SJ-F750SP-BK Service Manual

SJF800SPSL

[4] DIAGNOSIS METHOD OF FAILURE AROUND PWB

First of all, check by using the self-diagnosis.
In case that the power supply doesn't enter, check by the following procedure.
1. Disconnect power supply and check the following point.
• Is there any failure portion in inserting connectors?
2. Detach the PWB and check the appearance.
• Is there any burning or abnormal damage?
3. Check the conditions of the fuse and the varistor. (Fuse and varistor are located at the position in the figure.)
• Under the condition of power supply plug connected;
In case of no cooling and no indoor lamp lighting, there might be a possibility of fuse (F1 or F2) melt down.
When the fuse F1 or F2 is melt down, PWB does not operate at all.
When the fuse F3 is melt down, defrosting heater and refrigerator door heater are not electrified. (Defrosting error will be diagnosed as
"Defrosting failure" by the self diagnosis.) In this case, the cooling performance may deteriorate or dew generation may occur on the door,
because the defrosting is not done.
• Melting in the fuse cannot be checked visually (as the safer one than transparent glass tube is used). Be sure to detach the connector "CN1"
before measuring the resistance between the both ends of the fuse by the tester.
• Next, measure the resistance value between the both leads of the varistor.
Fuse 1
Varistor 1
Fuse 3
Fuse 2
Varistor 3
Flow of excessive current is considerable for some rea-
sons.
Melting
Check for any portion to cause short circuits especially on
the primary circuit.
Fuse
Fuse and varistor are normal.
Possibility to be caused by excessive current or voltage
Conduction
near the power supply is low. Proceed to the other check
item.
4. Check whether the temperature (resistance value) shown by R-thermistor is correct or not. (Refer to the table below.)
• Detach the connector "CN4" on the PWB and measure the resistance between 1 and 2 pins of harness side.
5. Check whether the temperature (resistance value) shown by Def-thermistor is correct or not. (Refer to the table below.)
• Detach the connector "CN5" on the PWB and measure the resistance value between 6 and 7 pins of harness side.
6. Check whether the temperature (resistance value) shown by F-thermistor is correct or not. (Refer to the table below.)
• Detach the connector "CN5" on the PWB and measure the resistance value between 4 and 5 pins of harness side.
Normal (over approx.1.5MΩ)
Varistor
There is a possibility of excessive voltage applied from out-
side with the factor such as thunder etc. When repeated with a
factor other than thunder, there might be the apparatus near
by generating noises.
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8 – 2
Damage