Facit 4431 Service Instruction page 27

Timing diagram for H-sync, V-sync and Video.
A)
0.5ms 20ms
B)
----i..J
0.5ms 16.7ms
LJ
C)
12us 64us
D)
____r-1
0.6us
SIGNAL NAME LOGIC LEVEL AT X4
A) V-SYNC 50Hz
X4-1 5V
B) V-SYNC 60Hz X4-1 5V
C) H-SYNC
X4-2 5V
D) VIDEO X4-4 appr. 1-2V
If the video and sync signals are not present,
check the logic power supply voltages at X3 on
the main logic board.
X3-1
X3-2
X3-3
X3-4,5
X3-6
X3-7,8
+17 Volts
+12 Volts
-23 Volts
+5 Volts
-12 Volts
Ground
If these voltages are correct, then the Main
logic board is faulty. If these voltages are
not correct check the mains fuse, if the fuse
is good, then the power supply should be repla-
ced.
9.5 DISASSEMBLY
Before attempting to gain access to the inter-
nal circuitry, TURN OFF THE POWER AND UNPLUG
THE LINE CORD.
1 There are four slot-head fixing screws which
retain the display unit top cover. These are
located at the bottom of the cover, under
the lip, close to where the stand enters the
display unit body. The screws can be acces-
sed from below by means of a short screw-
driver. To remove the cover the screws must
be screwed IN (clockwise) as fas as they
will go.
2 Grasp the lip of the cover on each side,
pull outwards and simultaneously lift the
cover.
3 Replacement of the cover is the reverse of
the removal. The retaining screws must then
be screwed OUT (anticlockwise) as far as
they will go.
27
9.5.1 MONITOR REPLACEMENT
The Monitor may quickly be replaced by unscrew-
ing the four retaining screws that fasten it to
the cabinet, disconnect the wiring harness from
the power supply and the ten pin connector from
the Main Logic and remove the CRT assembly by
tilting it back and lifting it up carefully.
The above operation should be reversed to in-
stall the replacement monitor.
CAUTION: When handling a monitor that has been
turned on recently (in last hour), care should
be exercised to avoid touching the dag or enve-
lop discharge lead. The picture tube is a capa-
citor and when operating, or recently thereaf-
ter this led has a very high voltage on it.
9.5.2 MAIN LOGIC BOARD REPLACEMENT
The Main Logic Board is secured to the rear co-
ver by seven screws.
9.5.3 ACCESS TO KEYBOARD
Switch off the unit and disconnect the key-
board from the display unit.
2 Remove the two retaining screw at the right
hand end of the keyboard, and then remove
the end cap.
3 Slide out the printed circuit board (discon-
necting the loudspeaker lead if necessare)
and lift off the top plate.
4 Reassembly of the keyboard is the reverse of
the above. Ensure that the p.c.b. and top
plate slide in the retaining grooves in the
keyboard housing.
9.6 ADJUSTING THE MONITOR
The terminal should have been powered on for
about 15 minutes before any adjustment is per-
formed, also the +12 Volt to the Monitor should
be checked, and if necessary adjusted to +12
Volt +/-0.6 Volt.
Adjustments are to be performed with Video sig-
nals at default value (normal Brightness).
• VERTICAL LINEARITY CONTROL
No character shall vary in height by more
than +/- 10% of the average height of all
characters in a row or column respectively.
e VERTICAL SIZE CONTROL
This control is used to adjust the size of
the display on the vertical axis. Adjust the
Vertical size (height) to 6" +/- 0.2". (This
adjustment should be performed in 60Hz mode).