Schematic Diagrams: November 2021

Tuesday, November 9, 2021

Daewoo 715B XGA COLOR MONITOR – How to enter the service mode, How to troubleshoot, Full schematic diagram

Always respect voltages. While some may not be dangerous in themselves, they can cause unexpected reactions that are best avoided. Before reaching into a powered TV set, it is best to test the high voltage insulation. It is easy to do, and is a good service precaution.

This color monitor automatically scans all horizontal frequencies from 30KHz to 70KHz, and all vertical frequencies from 50Hz to 160Hz. This color monitor supports IBM PC, PC/XT, PC/AT, personal System/2 (PS/2), Apple Macintosh, and compatible users crisp text and vivid color graphics display when using the following graphics adapters : (VGA, 8514/A, Super VGA, VESA and XGA and Apple Macintosh Video Card). And so, this color monitor has a maximum horizontal resolution of 1280 dots and a maximum vertical resolution of 1024 lines for superior clarity of display.
By accepting analog signal inputs which level is zero to 0.7 Volts. This color monitor can display and unlimited palette of colors depending on the graphics adapter and software being used.

Degaussing is always required when adjusting purity or convergence.
• The white balance adjustment has been done by a color analyzer in factory. The adjustment procedure,
described in the service manual is made by a visual check.
• Allow 20 minutes warm-up time for the display before checking or adjusting only electrical
specification or function.
• Reform the lead wire after any repair work.

Caution For Servicing
• In case of servicing or replacing CRT, high voltage sometimes remains in the anode of the CRT. Completely discharge high voltage before servicing or replacing CRT to prevent a shock to the serviceman.

ALIGNMENT PROCEDURE

Standard Adjustment Conditions
1. Power source voltage : AC 120V, 60Hz/AC 220V, 50Hz.
2. Aging : Take at least 20 minutes warm-up time.
3. Signals.
Video : Analog 0.7Vpp 75Ωterminal positive polarity
Synchronizing : TTL Level Negative/Positive Separate/Composite
Deflection frequency
Horizontal Frequency : 30KHz - 70KHz
Vertical Frequency : 50Hz - 160Hz
Pre-Adjustment
1. High Voltage Adjustment
Adjust 25.8 KVdc between Anode cap and ground at a cross hatch pattern of 60KHz by using VR 601.
2. H.Size Adjustment
(a) Receive a cross hatch pattern of 60KHz
(b) Set the H-Size control to the maximum on OSD menu.
Method to launch the factory mode [Service mode]
Push the menu button.
Push the menu button and plus control button ( + ) for 5 times in same time.
Main Adjustment.
1. Setting the Controls
Set the value of items as following.
Contrast : Max. (OSD value up to 100)
Brightness : Center (Set the OSD value to 50)
2. H.size, V.size, H.phase, V.position, Pincushion, Trapezoid
Receive the cross hatch pattern of Factory preset mode.
H.size, V.size, H.phase, V.position, Pincushion, Trapezoid are adjusted at each mode.
In Factory, Auto Alignment was done at each mode. Therefore, Factory preset mode has it’s own value according to each control.
3. Focus
(a) Set brightness control to center and contrast control to MAX.
(b) Receive all “H” character pattern of 60KHz mode signal.
(c) Adjust the Focus control of FBT to obtain best Focus (static focus and Dynamic focus).
4. Geometric Distortion Adjustment
(a) Receive the cross hatch pattern of VGA mode signal by using the signal generator.
(b) Pin balance, Parallelogram are adjusted the best geometric status.
(c) Repeat the adjustment at each mode.
5. White Balance Adjustment
(a) Receive a full white pattern of 60KHz mode.
(b) Set the bright control and contrast control to the maximum and receive the all black pattern.
(c) Adjust the G1 control in Factory mode to 0.8 Ft/L.
(d) Select the R, G, B Bias on the OSD menu and adjust the +/– key to get the color coordinates in X=0.281, Y=0.311.
(e) If the screen luminosity is changed, repeat (c) & (d) to get the 0.8 Ft/L screen luminosity.
(f) Set the brightness control to the center and contrast control to the maximum.
(g) Receive a full white pattern.

(h) Select the R, G, B gain on the OSD menu and adjust the +/– key to get the color coordinates in X=0.281±0.02, Y=0.311±0.02.
(i) Adjust the sub contrast (ABL) control to get the screen luminosity to 30.0 Ft/L.
6. Static Convergence Adjustment
(a) Apply a magenta cross hatch pattern on display.
(b) Adjust the focus from the best over all focus on the display.
Also adjust the brightness to the desired condition.
(c) Vertical red and blue lines are converged by varying the angles between the two tabs of the 4-pole magnets.
(d) Horizontal red and blue lines are converged by varying the tabs together keeping the angle between them constant.
(e) Apply a yellow cross hatch pattern on the display.
(f) Vertical green and red lines are converged by varying the angle between the two tabs of the 6-pole magnets.
(g) Horizontal green and red lines are converged by varying the tabs together and keeping the angle between them constant.