Testing For Dark Screen - Sony KD-34XBR2 Training Manual

Testing for Dark Screen

A dark screen with normal sound can be caused by the items listed in Chart 21-3. Use Figure 21-3 of the D board
in conjunction with Chart 21-3 to locate the test points.
Cause Board
Screen Screen
voltages too adj. on
low Chassis
Video A, B
blanking
No HV D, A, or G
CN8006/10
D Bd.
FBT
D8038
Chart 21-3 – Common Causes of a Dark Screen
Reason
IK blanking brings all CRT
cathodes high if a screen
voltage is low
RGB cathode voltages stay
abnormally high at 200Vdc
No HV or too low.
Figure 21-3 - D Board
Convergence ICs
CN8016/pin 3 = 7.46V
21. RA-5A Chassis High Voltage Stage
Troubleshooting Procedure
1. Look at each CRT. If there is an IK line at any
CRT, there is HV and deflection. If there is a
line missing, CRT drive is missing from the A
board.
2. The screen control is above the speakers.
Turn one at a time until retrace lines appear
then back off
3. Check for a sample of the HV at CN8016/pin 3
=7.46Vdc if the HV is normal. 0V if there is no
HV.
CRT screens
98
IK line
should
always be
present