NEC DPro2070SB, Service Manual

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3.2.7 Focus Failure
Does the focus become optimal in the center of the screen when
the focus VR of the FBT is adjusted?
OK
NG
Expected failure point
T701 (FBT), CRT socket or screen lead
OK
NG
Expected failure point
The focus leads; T701, CRT socket or CRT
Check the dynamic focus waveform.
Check the dynamic focus waveform at R7A2 on the MAIN PWB.
Vertical dynamic focus waveform oscillation voltage is approx. 200Vp-p (VGA480).
Horizontal dynamic focus waveform oscillation voltage is approx. 500Vp-p (VGA480).
(Note: The measurement condition should be as follows.
Resist pressure: 1000V
Capacity: 2pF
100:1 probe should be used for the measurement.)
OK
Check voltage waveform at Pin 4 of CN600.
The horizontal and vertical waveforms are inadequate.
Expected failure point
T7A1
The horizontal waveform
is inadequate.
The vertical waveform is inadequate.
Expected failure point
T701 (FBT) or CRT
OK
Expected failure point
IC601 or peripheral circuits
OK
NG
Check the voltage waveform at the base of Q7A1.
Expected failure point
IC6A2 or peripheral circuits
NG
Expected failure point
T7A1
NG
Expected failure point
Q7A1, R7A3-R7A6 or D7A1
OK
Check the voltage waveform at the emitter of Q7A1.
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Check the high voltage (HV).
Check the screen voltage.
Measure the high voltage. Usually it is maintained at 27
±
0.5KV.
Measure the screen voltage at CN201 on the CRT PWB. Usually,
it is maintained at 600 to 800V.
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