Sony CPD-G400 Training Manual page 81

4. Symptom – A color is too weak or bright.
The problem area can be in the DC bias voltage applied to the CRT cath-
odes or in the RGB drive signal that is AC coupled to the CRT cathodes.
We will stop the drive to see if we can get equal DC bias voltages at the
RGB cathodes to produce a white screen.
Procedure: Place the monitor into the aging mode or just feed in a dark
screen input (just sync). Increase the brightness and turn down the con-
trast (picture/drive) level. Increasing brightness just uses the cutoff con-
trol IC to bias the RGB CRT cathodes with a DC voltage. These cathode
pins should now be at the same voltage.
RGB Cathode
Voltages at the CRT
All the same RGB drive
problem
One is different One CRT cathode
is weak
5. Symptom – One or more colors flicker intermittently.
a. Inspect the video cable for bent pins, cuts and stains (liquid damage).
b. Often the solder connections break loose at the video-input jack where
it meets the circuit board. Resolder all the connections.
c. Tap the circuit board with an insulated tool like a pencil eraser. The
closer you get to the bad solder connection, the more often the prob-
lem will appear. Resolder the area.
6. Symptom – Ghosts or shadows in the picture.
Excessively long cables going to the computer or a loop through box is
used to run more than one monitor.
7. Symptom – Retrace lines present in the picture.
a. G2 voltage is too high.
b. Cut-off control driver IC or support parts are defective. Check all volt-
ages about the cut-off control IC and compare them to the voltages
listed in the schematic.
Problem Area
Monitor Screen
White Color dominant
output CRT is bad
RGB Cut Off IC, its
peripheral parts or RGB
background memory
data is defective/corrupt.
8. Symptom – Intermittent cut-off control IC failure.
Arcing in the CRT can cause repetitive failure of this cut-off control IC and
(zener) diodes that protect the RGB signal from the Output IC.
9. Symptom – Can only focus in the center or at the sides but
not both.
The dynamic focus circuit is not working. Look for a loss of focus wave-
form in this circuit.
10. Symptom – Front panel pushbuttons have no effect.
One of these buttons is shorted (on) and locking out the others.
Liquid/food is solidified, holding a button in.
11. Symptom – Two thin black lines are always on the CRT. They
never move.
These damper wires in the CRT are necessary for support. These very
thin horizontal lines are normal in a high quality Trinitron picture tube.
12. Symptom – Picture remains readable only during boot up.
Sync is lost after entering a Windows program.
a. The software from the computer is instructing the graphics card to
output sync at a higher (or lower) frequency than the monitor's normal
operating range.
b. The plug and play (DDC) communication is defective. This serial com-
munication from the monitor tells the computer what frequencies the
monitor is capable of. As a result, the computer's video card should
not generate a frequency beyond this range to cause this problem.
vi
Damper
wires