Abnormal Video On Crt Screen (Too Dark Or Too Bright) - NEC MultiSync FP1370 Service Manual

2. ABNORMAL VIDEO ON CRT SCREEN (too dark or too bright)

* Input 1/4 window pattern.
Set up BRIGHTNESS:preset, CONTRAST:max. and R/G/B control:all max. at OSM menu.
Measure R/G/B video outputs at TP-R, TP-G and TP-B on the CRT PWB (PWE-567C).
Check R/G/B
Normally, R/G/B video output voltages are approx. 45Vp-p with 1/4 window pattern input
video output
when the contrast control of the OSM menu is MAX.
NG
Check IC721
output (VIDEO)
NG
Check 80V line
OK
Check Vbb line
and 12V line
OK
Check IC721
input (VIDEO)
NG
Check IC711
output (VIDEO)
CONTINUE 1 CONTINUE 2
Measure the video output at IC721 pins 6(R), 14(G) and 4(B) on VIDEO
PWB (PWE-567A).
Normally, the wave form is same as upon figure.
OK
C729R/G/B failure, or CN-SG Failure.
Measure the voltage at CNP 3 on the VIDEO PWB(PWE-567A).
NG
CN-P failure, or check SW-REG (see item 13)
1) Check the voltage at C726 on the VIDEO PWB(PWE-567A). The voltage
is approx. 9.1V
2) Check the voltage at R728 (reverse of ZD721) on the VIDEO PWB
(PWE-567A). The voltage is approx. 12V
NG
1) ZD721, C726, R728 failure.
2) CN-AF failure.
Measure the video input at IC721 pins 8(R), 12(G) and 2(B) on VIDEO PWB
(PWE-567A). The voltage is approx. 5Vp-p.
OK
IC721 failure.
Measure the video output at IC711 pins 32(R), 29(G) and 35(B) on VIDEO
PWB (PWE-567A). The voltage is approx. 3Vp-p.
45 Vp-p
.
DC
7-4
.
DC