Sanyo SM-GA0005 Breakdown Analysis and the Means of Overhauling, Examining the Breakdown Causes

Fig.5-1

5. BREAKDOWN ANALYSIS AND THE MEANS OF OVERHAULING

Before overhauling a microwave oven, you should judge the breakdown and the cause correctly, then you can repair it with corresponding ways. The overhauling must be proceed in order, any hasty conclusion is not recommendable, otherwise over-working would be done when repair. The microwave oven may occur compound breakdown due to all kinds of different reasons, thus, when overhaul, they all should be taken into consideration. Special attention must be given to the microwave leakage and the electric insulation when examine because they may do harmful to the repairing staff.

5.1EXAMINING THE BREAKDOWN CAUSES.

How to examine a microwave oven with breakdown? A better means which demonstrated in practical operating are through inspecting and listening. On the basis of large amounts of perceptual knowledge, you can judge and analysie the break down quickly and correctly.

5.1.1INSPECTION.

Inspect whether the oven shape is disordered and where is the disordered position, If any. It is normal if the cabinet disordered a little, but abnormal if the oven, the door disordered, the door hook broken, the door crooked, or there are too much looseness between the door and the oven after the door is closed .

5.1.2LISTENING.

Listening to the sound of the oven operating and the noise of the fan. Minor “wen wen” noise, cycling“kala”noise and “shishi” noise should be considered as normal. But it is abnormal if the following noises occur:

(1)Sound “wen wen ” noise.

(2)Long time “shishi” noise.

(3)Strike sound like “Pipa pipa”

5.2 SPOT EXAMINING STEPS OF THE MICROWAVE OVEN

5.2.1 EXAMINE THE MICROWAVE INSULATING RESISTANCE
Measure the insulating resistance with a avometer or a
megaohmmeter the value should not be less than 2 megaohms.
Otherwise, part examination should be taken at once. Such as
checking whether the motor, the thermal cutout, the transformer or	glass tray
the capacitor are electricity leaking.

5.2.2EXAMINATION OF THE RESISTANCE VALUE OF THE MICROWAVE OVEN.

Close the door, set the time (the oven is at operating condition but the power plug haven’t been plugged in ), measure the two feet (L - N) of the power plug with R×1 grade of an avometer, the resistance value should be about 2.5 ohm. If open circuit occurs, then you must

check whether the 8A fuse is broken、the primary winding of the transformer is open circuit、the thermal cutout is open circuit or not, you must check whether the interlock device is put through or all the plugs are connected well. If short circuit occurred or the resistance less than 1.5 ohms, you

should check whether the primary winding of the power transformer is short – circuited or part short – circuited.

5.2.3EXAMINATION OF MICROWAVE LEAKAGE.

Measure the microwave leakage with a microwave leakage measure. Place a graduate of 275ml water at the middle of the glass tray of the oven (FIG.5 - 1). Close the door, power set high, time set to 3 minutes, press the starting button to operate the oven. After rectified the microwave leakage measure, measure around the door crack, those hole position of the window and the air vent at four sides of the oven with the probe of the measure. When measure, the moving

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