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Sony KV (BG-3R) XA34M31

Sony KV (BG-3R) XA34M31

Mark RobertsonAbout 3 minCRT RGB modKV-XA34M31KV-XA29M31KV-XA29M50

Sony KV-XA34M31 (BG-3R) chassis CRT RGB mod

Below mod was performed on a 34" Sony KV-XA34M31 by Mark Robertson. BG-3S chassis is identical to BG-3R and the below RGB mod method can be applied to it as well.

Sony BG-3R

This set supports composite, s-video and component natively. After the below modification, it also supports RGB via SCART input.

CRT safety


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.


Service manuals


Sony KV-XA34M31

  • 220-240V, 50/60Hz, 185W, Manufactured in Malaysia
  • Chassis: BG-3R
  • Tube: Sony Trinitron A80LPD90X (Made in USA)
  • Jungle Chip: CXA2159S
  • OSD Chip: CXP750097-032S

Performing the RGB 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. Taking out the chassis is fairly straight forward on this CRT. There are few wires that needs to be disconnected.

  1. Degauss wire
  2. Power wire
  3. Ground wire attached to the neck board
  4. Yoke deflection coil wire
  5. Anode wire (this is the one with the rubber cap)
  6. Left and right audio wires

Please remember that wires 1-5 are critical for the CRT to function and should not be omitted. Having any of these wires disconnected while powering up can damage the board and can have adverse effects.

It should also be noted, the B board (smaller board) should be removed to solder audio, sync and ground. The A board (bigger board) doesn’t need to be removed but does need to be on its side so you can remove the R063, R064 and R065 resistors.

Mux diagram

Sony BG-3R

STEP 1: Remove the following components

Closed caption card (teletext) and OSD shares the same RGB input on the chroma. Therefore, this is not going to be a direct injection. It still requires the removal of the three (470Ω) ground resistors on the OSD side.

  • R063 (470Ω)
  • R064 (470Ω)
  • R065 (470Ω)

Sony BG-3R

STEP 2: Connect RGB, Blanking and Ground

We are going to get rid of the closed caption (teletext) card and tap into the RGB input there.

Sony BG-3R

The CN801 connector was salvaged. Sony BG-3R

R, G, B, Blanking and Ground wires were soldered to this connector. Sony BG-3R

The connector was reinserted into the board. Sony BG-3R

STEP 3: Connect Audio and Sync

Soldered sync to the S-Video luma pin. Sony BG-3R

Note: S-video and audio dummy plugs are required for sync and stereo audio.

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.

Buy your RGB mux board

RGB mux boardKV-XA34M31
Audio LR (R7, R8)1kΩ
RGB termination (R1, R2, R3)75Ω
RGB inline resistors (R4, R5, R6)560Ω
Diode (R9)1N4148
Blanking Ground Resistor (R10)--
Blanking Resistor (R11)short
CRT modificationKV-XA34M31
Add diodes to RGB lines on Board ANo

Sony BG-3R

Sony BG-3R

STEP 5: Attach the female SCART connector to TV

Creating a SCART cutout and mounting it is an art. I have a dedicated section for it. How to create and mount a SCART female plug?

This SCART port was cut a bit rough. You can make the SCART port look smoother with a file. Sony BG-3R

Sony BG-3R

Sony BG-3R

Horizontal Position Adjustment

In some cases, especially on larger screens, the picture will not be centered even after adjusting HPOS to 0 or to its maximum value. To get around this, you can try adjusting this lever, which will shift the picture horizontally. Sony BG-3R


Spyro The Dragon Sony BG-3R

Crash Bandicoot Sony BG-3R


240p - SMPTE Sony BG-3R

240p - Pluge Sony BG-3R

240p - Grid Sony BG-3R

240p - RGB Sony BG-3R


TV off Sony BG-3R

B Board Sony BG-3R

A & B Boards Sony BG-3R

Back Label Sony BG-3R

Tube Sony BG-3R

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