NEC DPro2070SB, Service Manual

Page: 97 / 108

3-23
CONTINUE 1
Check the output waveform of pre-AMP.
Expected failure point
IC211 on the VIDEO PWB
NG
OK
Measure the waveform at R/G/B output Pins 25, 27
and 29 of IC211 on the VIDEO PWB.
Expected failure point
L211R/G/B or R211R/G/B
Check the R, G, B video outputs.
Measure the voltage waveform at R200R/G/B on the CRT PWB,
and confirm whether BLACK LEVEL voltage is maintained at
approx. 60-90V.
Measure the voltage between GND and + electrode of C260.
NG
Check the voltage of C210R/G/B on the VIDEO PWB.
OK
Check the 215V line.
Expected failure point
CN211 or 215V line of power circuit
OK
Confirm the voltage is approx. 60-100V.
NG
OK
Confirm the voltage at the base of R250R/G/B is approx. 6V.
Expected failure point
R261, D264, R260 or peripheral circuits
NG
OK
Expected failure point
Q250R/G/B or Q251R/G/B
Expected failure point
L200R/G/B or L201R/G/B
Check the HV operation.
Confirm whether the HV is 27
±
0.5KV.
Expected failure point
The HV circuit (See Item 3.4.4)
NG
OK
Check the heater voltage.
Measure the voltage at both terminals of C203H on the CRT PWB.
Usually, the voltage is approx. 6.3V.
Expected failure point
1) CN211
2) The switching power circuit (See Item 3.4.1)
NG
OK
Check the screen control of FBT.
Confirm the voltage of R205S on the CRT PWB is approx. 600-800V.
NG (too low)
Expected failure point
T701 on the MAIN PWB or CRT socket on the CRT PWB
OK
Expected failure point
CRT
NG
CONTINUE 2
BLACK LEVEL