LG LTM9020B, Service Manual

Page: 22 / 43

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COMPONENTS TEST PROCEDURE RESULTS
H.V.Diode (rectifer) STEP 1. Test the diode to see if it is shorted.
Procedure:
1. Select the
Ω
scale on the meter.
2. Place the meter leads across the diode as
pictured in Figure 14-a. The reading should be
“40M
Ω
,” “OL,” or a reading of infinity.
3. Reverse the meter leads. The reading should
again indicate a reading of infinity. If the diode
shows “infinity” in BOTH directions, it is NOT
shorted.
4. If the diode is not shorted, proceed to step 2.
STEP 2. Test the diode for forward biasing.
Procedure:
1. Select the DCV scale on the meter.
2. Using the meter, battery, and jumper wire,
connect the items as illustrated in Figure 14-b.
This has the positive side of the battery
connected to the cathode of the diode.
3. The diode should be forward biased therefore
a voltage reading of approximately 4.7 VDC to
6.4 VDC will be read depending on meter, battery
strength, etc. (Note: If the meter leads were
reversed, a negative voltage of the same amount
would be seen.)
STEP 3. Test the diode for reverse biasing.
Procedure:
1. Using the same scale on the meter, connect
the positive side of the battery to the anode of the
diode as illustrated in Figure 14-c.
2. The diode should be reverse biased therefore
a reading of 0 volt or a value displayed in mV will
be seen. (The display will be erratic changing
values rapidly in the mV scale.)
Normal:
Approximately
4 .7-6.4V
Normal:
Approximately 0V
Figures 14-a Figures 14-b Figures 14-c