Purity Adjustment; Convergence Adjustment - Sharp 20CT-250 Service Manual

PURITY ADJUSTMENT

No. Adjusting point Adjusting procedure/conditions
1 Purity 1. Using the remote controller, make the screen colour
adjustment green-only. Adjust the contrast control to have a beam
current of about 700 µA.
2. Degauss the cathode ray tube enough with the
degaussing coil.
3. Keep the purity magnet in the zero magnetic field
in advance. Roughly adjust the convergence.
4. Observe the points "a" and "b", as shown in Fig.
5-1 , through a microscope. Adjust the landing to
the rank "A" requirements.
5. Adjust the raster rotation to "0" eastward.
6. Tighten up the deflection coil screws.
» Tightening torque: 108 ±20 N (11 ±2 kgf)
7. While observing the cathode ray tube corners.
apply the magnet sheet to have the landing at
rank "A".
Note: Before starting this adjustment, warm
up the unit for 30 minutes or longer at
a beam current of over 700 µA.
Note: Set the service switch S1001 to call the
service mode and press the single-col-
our key on the process remote control-
ler to get the green-only screen.
* Each time the single-colour key is pressed, the
screen colour changes as follows.
Green-only Blue-only
screen screen
Single-colour
screen cleared
Waveform and others
a
b
Fig. 5-1
A
B
A = B
Fig. 5-2
Rank "A" (on the
right of the CRT)
A
Red-only
screen
B
A = B
Fig. 5-3
Rank "A" (on the
left of the CRT)
* Whether in the service mode or
not, hold down the single-colour
key for 1 second or longer and
the service mode is called.
The TEXT key or the R.G.Cy key
may be used instead to provide
the single-colour screens.
7-1

CONVERGENCE ADJUSTMENT

No. Adjusting point Adjusting procedure/conditions
1 Convergence 1. Receive the Crosshatch Pattern signal.
adjustment 2. Using the remote controller, call the Normal mode.
(to be done
after the purity STATIC CONVERGENCE
adjustment) 1. Turn the 4-pole magnet to a proper opening an-
gle in order to superimpose the blue and red col-
ours.
2. Turn the 6-pole magnet to a proper opening an-
gle in order to superimpose the green colour over
the blue and red colours.
DYNAMIC CONVERGENCE
1. Adjust the convergence on the fringes of the
screen in the following steps.
a) Fig. 6-1 : Drive the wedge at point "a" and
swing the deflection coil upward.
b) Fig. 6-2 : Drive the wedges at points "b" and
"c" and swing the deflection coil downward.
c) Fig. 6-3 : Drive the "c" wedge deeper and
swing the deflection coil rightward.
d) Fig. 6-4 : Drive the "b" wedge deeper and
swing the deflection coil leftward.
2. Fix all the wedges on the cathode ray tube and
apply glass tape over them.
3. Apply lacquer to the deflection yoke lock screw,
magnet unit (purity, 4-pole and 6-pole magnets),
and magnet unit lock screw.
Finally receive the red-only and blue-only signals
and make sure there is no other colour mixed on
the screen.
Waveform and others
BGR
Fig. 6-1
RGB
Fig. 6-2
RGB
B
G
R
Fig. 6-3
BGR
R
G
B
Fig. 6-4
Wedge "a"
About
100°
Lacquer
Wedge
"b"
Fig. 6-5
4-pole magnet
6-pole magnet
CRT neck
Lacquer
Purity magnet
Fig. 6-6
7-2
B
G
R
R
G
B
About
100°
Wedge
"c"