Tandy CM-8 User Manual

5. High Voltage Check
High voltage is not adjustable but must be checked to
verify that the Monitor is operating within safe and ef-
ficient design limitations as specified .
1.
Operate the Monitor for at least 1 5 minutes at
1 20VAC line voltage with the computer display-
ing a white pattern.
2. Turn off switch SW851 on PCB-B.
3. Rotate the screen control (on T602) to the maxi-
mum (counterclockwise) end of its rotation .
4. Connect an accurate, high-voltage meter to the
CRT anode. Check that the reading is approximate -
ly 22 . 0kV to 23 . 0kV (at 0 beam current) .
If a correct reading cannot be obtained, check the cir-
cuitry for malfunctioning components. On comp letion
of the voltage check, readjust the screen control for
proper operation as detailed in the "Black and White
Tracking " procedures.
6. Vertical-Linearity Adjustment
1. Operate the computer in such a way that the let-
ter "H" covers the entire screen (data display peri-
od :
44.698 µS hori zonta l, 14.331 mS vertical) .
2. Adjust the V-Lin . control (R526) until the height
of a character varies no more than 10 percent from
the average character size.
7. X-ray Protector Circuit Test
After service has been performed on th e horizontal
deflection system , the high voltage system and the X-
ray
protector circuit must be tested for proper opera-
tion as follows:
1. Apply 1 20V AC, using a variac transformer .
2.
Operate the computer in such a way that the en-
tire screen displays a white signal, (data display
period: 44 . 698 µS horizontal, 14 . 331 mS vertical).
3.
Check the voltage of test point TP601. (Its voltage
should be about 18.5V DC .)
4. Connect the cathode of the D 504 and TP601
through a short clip lead. Then, connect another
short clip lead between both sides of R 522 . The
operation of the horizontal oscillator is stopped by
connecting these points.
5. To start the operation again, remove the two short
clip leads and connect TP602 and chassis ground
(TP702) using a short clip lead. Disconne ct the
short clip lead as soon as the Monitor operates
again with a normal picture.
6. If the operation of the horizontal oscillator does not
stop in step 4, the circui t must be repaired before
the set is returned to the customer .
17
8. Color Purity Adjustment
The Monitor must have been operat ing 1 5 minutes pri-
or
to this procedure, and with the faceplate of the CRT
at room temperature. The Monitor is equipped with an
automatic degaussing circuit. However, if the CRT
shadow mask has become exces siv ely magnetized, it
may be necessary to degauss it with a manual coil. (Do
not switch the coil off while the raster shows any ef-
fect from the coil.)
1. Check for the correct location of all neck compo-
nents. Refer to Figure 13.
2. Rough in the static convergence at the cen ter of
the CRT, as explained in the static convergence
procedure .
3.
Rotate the contrast control to the center of its
range and rotate the brightness control to its max -
imum clockwise position.
4. To obtain a blank raster, disconnect E (Signal in-
put) from PCB-A .
Rotate the screen control (part of T602) clockwise
until a normal raster is obtained.
5. Rotate the red bias (R862) and blue bias (R864)
controls to the maximum counterclockwise po-
sitions.
Rotate the green bias control (R863) sufficiently
in a clockwise direction to produce a green raster.
6. Loosen
the deflection yoke clamp screw and pull
the deflection yoke as close as possible to the pu-
rity and convergence magnets assembly .
7. Begin the following adjustment with the tabs on
the round purity magnet rings set together. Initial-
ly,
move the tabs on the round purity magnet rings
to
the side of the CRT neck. Then, slowly separate
the two tabs while at the same time rotating them
to ad just for a uniform green verti c- al band at the
center of the CRT screen. Refer to Figure 12 .
8.
Carefully slide the deflection yoke forward to
achieve green purity (uniform green screen) .
Tighten the deflect ion yoke clamp scr ew.
Note: Center purity is obtained by adjusting the
tabs on the round purity magnet rings. Outer edge
purity is ob tained by sliding the deflection yoke
forward .
9.
Check for red and blue-field purity by reducing the
output of the green bias control (R863) and alter-
nately increasing the output of the red (R862) and
blue (R864) bias controls , and touch up the ad-
justment, if required.
10. Reconne ct E to PCB-A .
11 . Perform the "Black and White T rac king "
procedures .

Tandy CM-8 Specifications

General

Brand	Tandy
Model	CM-8
Category	Monitor
Language	English