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.033uF, 854
1N4005
1N4005
62K,852
G2
GREEN
10
11
13
14
15
16
17
18
19
20
GAPS
GND
BLUE
FIL.FIL.
RED
G1
903
0Ω, 904
10uF
1K
855
100K, CF
RED
853
0Ω, 898
0Ω, 896
0Ω, 897
.015uF
901
0Ω, 902
10uF
895
H400
899
906
+
7
6
5
8
9
10
11
12
1
5
6
7
8
9
10
11
12
2.2nF,889
470Ω, CF
905
1N4005
205Ω
62K,912
CRT
877
900
470Ω, CF
250V
CF
FR205
SOCKET
Video Board
XX93
18Ω, 879
+
Filament Voltage Test.
When replacing either the flyback transformer or the video
board, the filament voltage may not be correct.
Measuring the filament voltage is not accurate using a true
RMS voltage meter, because of the high frequency components,
which make up the filament voltage. An oscilloscope, with RMS
capability, may be used to measure the filament voltage.
Although a visual check of the filament color is a indicator of the
filament voltage, it is a good practice to check the filament voltage if
there is any doubt about this important monitor parameter.
The following filament voltage test is an accurate method of
finding the true RMS voltage to the filament. This is accomplished
by comparing the light output of the filament when it is driven by
the monitor to the light output of the filament with an applied DC
voltage using a loaded photocell.
SETUP:
To find the filament voltage;
1. Solder two short buss wires to the filament pins to clip on.
2. Use black tape to secure the photocell over the hole in
the plastic CRT socket connector. Caution: Be sure
not to move the photocell between the two tests.
3.
4.
Connect the variable voltage, 1 amp, DC power supply to the filament.
The negative lead to the filament ground at the CRT socket pin 10.
5.
Adjust the power supply voltage for the photocell reading, recorded in step 3.6.
The equivalent filament RMS voltage is now recorded by measuring the DC voltage
at the CRT socket pins 9 and 10.
Turn off the monitor.
7.
Record the DC voltage output from the photocell with the monitor running normally.
The monitor should be powered up for 10 minutes before making this measurement.
ISOLATED
DUAL 1A DC
POWER
SUPPLY
0 to 30V 0 to 30V
.150V
DVM
+6.30V
DVM
24.3K
+
++
CELL
98