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LO Get Kitlt)
| Troubleshooting Step 3:| Nothing appears on screen.
Possible Causes
o ~~ CRT high-voltage system failure
oO
Processor board failure
oO
CRT failure
Checks and Repairs
1)
Check that the CRT filament lights. Adjust the R510 brightness control on the display board.
following the steps below.
a)
Switch off the power and, taking care not to receive an electric shock from the high voltage,
pull out the CRT anode cap. (Do not touch the electrodes.)
b) — Bring the anode cap electrode to a position about 3/16" from the chassis (metal part). If
the high-voltage system is problem-free, a spark will jump between the chassis and electrode.
3)
Check the vertical and horizontal sync pulses using a osilloscope. If they are not present, there is
a failure on the processor board.
Vertical sync pulse (connector CN4-3 on processor board)
21.13 ms
= ee mee
OV
0.41 msec
(47.32Hz)
Fig. 61
Horizontal sync pulse (connector CN4 pin 4 on processor board)
5V
4.73use
os iio
41.11 psec
(24.325 kHz)
Fig. 62
4)
Use the oscilloscope to observe the signal at pin 1 of connector CN4 on the processor board.
A pulsed random signal, such as that shown in the figure below, should appear.
Approx. 5Vp-p
2.5 V~3.0 V
Fig. 63
5)
if there is no problem with the checks in 1), 2), 3) and 4) above, the CRT is malfunctioning and
should be replaced.
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