Specifications

Ver SG 9/200 28 Sharp Electronics Corporation
With an ohmmeter, check the resistance of the primary winding. A normal reading
would be less than one ohm. This reading is hard to detect on an analog meter as the
needle appears to indicate a short. However, if the reading looks close to the shorted
condition and the line fuse is not blown the winding is probably good. Of course, any
time resistance checks are being taken, the component should be isolated (wires removed
from terminals). This prevents the possibility of putting other resistance’s in parallel with
the component. giving false readings. The secondary is also checked with an ohmmeter.
The filament winding should indicate less than one ohm. The high voltage winding
should indicate anywhere from 50 to 200 ohms depending on the output rating of the
model oven you are checking. Be certain to refer to the service manual for the exact ohm
reading on the high voltage secondary as layer shorts are the most common problem with
power transformers (the winding reads 90 ohms on your meter but the service manual
states the reading should be 120 ohms, this is a layer short).
The rectifier is also checked with an ohmmeter. Set the analog meter on the X 10,000
scale. Place the negative lead of the meter on the cathode of the rectifier (the cathode is
the side to which the arrowhead points toward). A reading of 50,000 ohms is normal. If
an infinite reading or a low resistance reading is indicated the rectifier is defective.
Reverse the leads of the ohmmeter on the rectifier terminals (the negative lead on the
anode). This should indicate an infinite reading on the meter, any other reading would
indicate a defective rectifier.
The capacitor is also checked with an ohmmeter. Isolate the capacitor and place the
meter leads on the leads of the capacitor. With the meter set on the X 10,000 scale, the
needle should swing towards a lower resistance reading. As the capacitor charges the
resistance should increase to an infinite reading. Reverse the meter leads and the same
deflection should occur as the capacitor now charges with the reverse polarity. If the
meter indicates a constant resistance the capacitor is shorted or leaky. If deflection is not
present it indicates the capacitor is open.
If the transformer, rectifier, and capacitor check good refer to the magnetron section of
this manual for test procedure.