Sharp 27F640 (GB-3U)
Sharp 27F640 CRT RGB mod
This is a work in progress article.
CRT safety
Caution
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
Theory
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.
Service manuals
Mux diagram
Calculating the RGB external resistor value
Love it when we can put theories to use! Formula from our theory page!
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.
- R806 (680Ω)
- R807 (680Ω)
- R808 (680Ω)
STEP 2: Connect RGBs, Blanking and Audio
STEP 3: Add diode to the blanking
Find a way to introduce the diode such that current from external input doesn't flow to the OSD IC.
STEP 4: 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.
| TV Model | 27F640 |
|---|---|
| CRT inline resistors | 4.7kΩ |
| Removed ground resistor value | 680Ω |
| Add diodes to RGB inline? | No |
| Add diodes to blanking on chassis? | Yes |
| RGB termination (R1, R2, R3) | 75Ω |
| RGB inline resistors (R4, R5, R6) | 680Ω |
| Audio LR (R7, R8) | 1kΩ |
| Diode (R9) | 1N4148 |
| Open (R10) | -- |
| Blanking Resistor (R11) | shorted |
| Add diodes to RGB lines | Yes |
- Blanking resistor R11 can be shorted as long the blanking is injected in the correct place.