LG RF-20CC20M, Service Manual

Page: 13 / 27

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PURITY & CONVERGENCE ADJUSTMENT
Caution:
Convergence and Purity have been factory aligned. Do not
attempt to tamper with these alignments.
However, the effects of adjacent receiver components, or
replacement of picture tube or deflection yoke may require the
need to readjust purity any convergence.
¡
Purity Adjustment
This procedure DOES NOT apply to bonded yoke and picture
tube assemblies.
The instrument should be at room temperature (60 degrees F or
above) for six (6) hours and be operating at low beam current
(dark background) for approximately 20 to 30 minutes before
performing purity adjustments.
CAUTION:
Do not remove any trim magnets that may be
attached to the bell of the picture tube.
1. Remove the AC power and disconnect the internal
degaussing coil.
2. Remove the yoke from the neck of the picture tube.
3. If the yoke has the tape version beam bender, remove it and
replace it with a adjustable type beam bender (follow the
instructions provided with the new beam bender)
4. Replace the yoke on the picture tube neck, temporarily
remove the three (3) rubber wedges from the bell of the
picture tube and then slide the yoke completely forward.
5. Reconnect the internal degaussing coil.
6. Position the beam bender locking rings at the 9 o'clock
position and the other three pairs of tabs (2,4 and 6 pole
magnets) at the 12 o'clock position.
7. Perform the following steps, in the order given, to prepare the
receiver for the purity adjustment procedure.
a. Face the receiver in the "magnetic north" direction.
b. Externally degauss the receiver screen with the television
power turned off.
c. Turn the television on for approximately 10 seconds to
perform internal degaussing and then turn the TV off.
d. Unplug the internal degaussing coil. This allows the
thermistor to cool down while you are performing the purity
adjustment. DO NOT MOVE THE RECEIVER FROM ITS
"MAGNETIC NORTH" POSITION.
e. Turn the receiver on and obtain a red raster by increasing
the red bias control (CW) and decreasing the bias controls
for the remaining two colors (CCW).
f. Attach two round magnets on the picture tube screen at 3
o'clock and 9 o'clock positions, approximately one (1) inch
from the edge of the mask (use double-sided tape).
DEFLECTION YOKE
PURITY &CONVERGENCE
MAGNET ASSEMBLY
RUBBER
WEDGES
GLASS CLOTH TAPE
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PURITY MAGNET
6-POLE
4-POLE
4-POLE
MAGNET
CONVERGENCE MAGNET ASSEMBLY
6-POLE
MAGNES
PURITY MAGNET(2-POLE)
X-AXIS YOKE
POSITIONING
(L/R PURITY)
6-POLE
MAGNETS
CONVERGENCE MAGNET ASSEMBLY