Sony CPD-G400 Training Manual page 51

CRT Cathode current Measurement
All CRT cathode current must flow through IC004. A sample of this cur-
rent is represented by a signal at IC004/pins 10-12. Although this signal
consists mostly of a DC voltage that corresponds to a white screen, the
addition of a blanking pulse makes this an AC signal.
Ik/Aging signal
IC004/10-12
Each cathode's signal is rectified and the corresponding DC voltage is
applied to IC003/pins 20-22.
Drive Level Balancing
During the Ik measurement mode, IC003 translates the Ik analog volt-
ages that represent a white screen and sends them to CPU IC1001 one
color at a time. The original Ik voltages were stored as data in memory
when the monitor was new. The CPU compares the old and new Ik data.
If they do not match, data is output the CPU into IC001. IC001 increases
the R, G or B gain that correspondingly increases the Ik voltage from
IC004. IC003 sends new Ik data to CPU IC1001 for a second compari-
son. The process repeats until the new and old Ik voltages in IC1001
match. The gain level is stored into memory and used every time the
monitor is turned on. The procedure is then repeated for the other colors.
At the conclusion of image restoration, the CPU IC1001 sends IC003
data to discontinue the white screen and disregard the Ik voltages input
pins 20-22.
Summary of Video IC Operations & Voltages
IC Used In Modes
RGB Preamp Normal Display
IC001 OSD (Menu)
Aging
Ik image restore
Output IC002 Same as above
Blanking pulses
White screen
Function
RGB Preamplifier
RGB/OSD switch
Background Voltage D/A Conv
G2 Voltage D/A Conv
RGB Output voltage amplifier
45
OSD OSD (Menu)
IC003 Aging
Ik image restore
RGB Cutoff Normal Display
IC004 OSD (Menu)
Aging
Ik image restore
DC Voltages
Function
RGB signal Input IC001/pins 10-12
to IC001 (no signal is input in
the aging mode)
RGB signal Output IC001/pins 20, 23,
from IC001 27.
RGB Background IC001/pins 30-32
Output from IC001 Background Out
RGB Output from IC002/pins 5, 3, 7
IC002
Background Input IC004/pins 13-15
at IC004
Background IC004/pins 3, 5, &
Output from IC004 7.
Ik Output from IC004/pins 10-12
IC004
Ik Input to IC003 IC003/pins 20-22
OSD Output from IC003/pins 14-16
IC003
* The RED cathode was unsoldered for measurement comparisons. Red
drive voltages are unaffected but Ik voltages are lower.
Troubleshooting
See the troubleshooting checklist in the appendix portion of this training
manual.
Makes menu, graphics and a
white screen.
Performs Ik image
calculations.
Horiz & Vert video Blanking
Sets CRT cutoff voltage level
Measures Ik cathode voltage
Aging Mode *
Location Red * Green
1.9V 1.9V
2.7V 2.7V
3.8V 3.7V
43V 43V
4.77V 4.7V
111V 110V
0.35V* 0.507V 0.53V
1V* 1.95V
0.16V 0.16V
restore
Blue
1.9V
2.7V
3.2V
43V
4.6V
101V
2V
0.16V