Sharp 27L-S100 CRT RGB mod
This tutorial covers the RGB mod for Sharp 27L-S100. These instructions should also work for other SN91 chassis based Shartp CRTs.
You can die doing this! So read carefully! CRT TV is not a toy. Do not open a CRT TV. If you don't have any prior knowledge about handling high voltage devices, this guide is not for you. CRT TV contains high enough voltage (20,000+ V) and current to be deadly, even when it is turned off.
Plan of attack
Sometimes it is nice to know the theory behind the mod. I have put this on a separate page. This shows how the various resistor values are calculated.
- Manufactured: February 1999, New Jersey
- NTSC, 60 Hz
- Chassis: SN91
- Tube: A68ADT25X03
- Jungle Chip: IX3253CE
- OSD Chip: IX3256CE
IX3253CE Chroma Chip
If you are building your own circuit, this diagram should help
RGB external resistor value and Blanking voltage
Love it when we can put theories to use! Formula from our theory page!
For this particular mod we are going to use diodes inline to prevent signal reflection.
RGB external resistor value = 0.7 x (6800 + 75) - (75 x (5 - 0.7)) / (5 - 0.7 - 0.7) = (4812 - 322) / 3.6 = 1247 ohm
~ 1.2 Kohm resistors should do the job.
For this particular set, we are also going to use 220Ω termination resistance instead of the standard 75Ω resistance to achieve proper contrast levels.
We can find that chroma chip blanks at a voltage slightly higher than 1.5V using the existing resistance values used for voltage dividing. 6.8kΩ and 3.3kΩ. Since we are going to add a diode inline, we need to compensate for that voltage drop. We have to replace the 3.3kΩ resistor with a 4.2k achieve the same voltage levels. At 1.6V, OSD gain will be correct and allow the external RGB input on pin 15-17.
Performing the mod
Now that you roughly know what needs to be done, prepare for the mod. Place the board on a comfortable place. Make sure you are not putting pressure on the flyback or other components.
STEP 1: Remove the following components
Remove the following components. RGB resistors to the ground. Measure twice and mark before you remove.
- R803 (2.2 kΩ)
- R804 (2.2 kΩ)
- R805 (2.2 kΩ)
STEP 2: Connect RGBs, Blanking and Audio
Coax cable was used for this particular mod. This is optional and only needed if you care every bit about the interference. Using the standard unshielded ribbon cable should be sufficient, however that might not always work well.
Make sure to install inline diodes on R, G, B and another diode on blanking right after the 6.8kΩ resistor to reduce signal noise.
Below picture was taken before and after adding the diodes.
STEP 3: Build your mux board
Below mod uses the RGB mux board. This is optional, but will make your mod easier and stable. You can also create the circuit presented in the schematics above without the board. Please also checkout the precalculated resistor values.
|Audio LR (R7, R8)||1kΩ|
|RGB termination (R1, R2, R3)||220Ω|
|RGB inline resistors (R4, R5, R6)||1.2kΩ|
|RGB inline diodes||1N4148|
|Blanking Resistor (R11)||6.8kΩ|
|Replace R802 (3.3kΩ)||4.2kΩ|
STEP 4: Attach the female SCART connector to TV
Creating a SCART cutout and mounting it is an art. There is a dedicated section for it.
After attaching the RGB mux board
Remote Control for this TV
Getting into service menu
While pressing the Vol-up and Ch-up buttons at the sametime, plug the AC cord into a wall socket.