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Sony KV (BA-4) 27V40

Kaz PackmanAbout 5 minCRT RGB mod

Sony BA-4 chassis RGB and YPbPr mod

Bring your Sony CRT to life with vibrant RGB colors!

BA-4D has a similar chassis and the tutorial for it can be found here.

If you're looking to get the most out of your Sony KV-27V40 Trinitron, you may want to consider modding it for RGB and component output. This guide will show you how to do just that.

Instructions below should also apply to these models:

  • Sony KV-27V40
  • Sony KV-27V45
  • Sony KV-27V65

Sony KV-27V40 Sony KV-27V40

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-27V40

  • Manufactured: February 1999, Mexico
  • NTSC, 60 Hz, 140W Max
  • Chassis: BA-4
  • Tube:
  • Jungle Chip: CXA2061S
  • OSD Chip: M37273MF

Mux diagram

If you are building your own circuit, this diagram should help. The diagram is for KV-27V40, it will also work for any other BA-4 chassis.

Sony BA-4 chassis RGB mod mux diagram

Calculating the RGB external resistor value

Formula from our theory page!


Calcualted 910Ω for 0.7Vp-p. With didoe inline for RGB, you have to use 1kΩ

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. 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.

Sometimes it can be overwhelming to see a large chassis. But, we are primarily going to focus on two areas.

Chassis from Sony 20S42 (BA-4D). BA-4 is a similar chassis. img

  • Area 1: This is where we are going to remove resistors and attach the R, G, B and blanking wires
  • Area 2: This is where we are going to connect composite, audio L, R and ground wires

STEP 1: Remove the following components

Zooming in on Area 1.

BA-4 chassis - KV-27V40 RGB mod

Remove the following components. RGB resistors to the ground. Please always measure and mark them, so that you know you are removing the correct partrs.

  • R087 (680Ω)
  • R088 (680Ω)
  • R089 (680Ω)

STEP 2: Connect RGBs, Blanking

Then attach the R, G, B and blanking wires to the respective legs of the diodes. Wires should be attached to the side closer to the jungle chip.

  • R, G, B wires are red, green and blue respectively
  • Thick blue wire here is used for internal blanking through the switch. If you are using the ribbon cable with external blanking, this would be the brown wire.

BA-4 chassis - KV-27V40 RGB mod

STEP 3: RGB inline diodes

To reduce interference, it is recommended to add these inline diodes. Heat shrink was used in the middle one to avoid shorts. BA-4 chassis - KV-27V40 RGB mod

STEP 4: Connect Sync and Audio

BA-4 chassis - KV-27V40 RGB mod

  • Thick yellow wire is for sync (luma)
  • Thick white wire is for S-Video detect
  • Purple and black wires are for ground
  • Grey wire is for right audio
  • White wire is for left audio

BA-4 chassis - KV-27V40 RGB mod

Full board BA-4 chassis - KV-27V40 RGB mod

STEP 5: Disconnect the VM cable to reduce artificial sharpening

The Velocity Modulation (VM) connector can be found on the neck board. Disconnecting this is recommended to get the best picture quality from your RGB and YPbPr mods. BA-4 chassis - KV-27V40 RGB mod

STEP 6: 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

TV ModelKV-27V40KV-27V42KV-27S42
Audio LR (R7, R8)1kΩ1kΩ1kΩ
RGB termination (R1, R2, R3)75Ω75Ω75Ω
RGB inline resistors (R4, R5, R6)1kΩ1kΩ1kΩ
Diode (R9)1N41481N41481N4148
Blanking Resistor (R11)1kΩ1kΩ1kΩ
Add diodes to RGB linesYesYesYes

On this particular CRT, Kaz chose to not use the external blanking signal. Instead, a switch was used to blank. Therefore, the blanking resistor (R11) and diodes (R9) are not populated. img

5V for blanking was tapped from this location. There are also other possible locations on the chassis where 5V can be tapped from. img

STEP 7: YPbPr mod

This mod uses the 3P3T switch for blanking between YPbPr and RGB Sony BA-4 chassis 3P3T Diagram

Remove 0.01uF caps C380, C381, C382 and populate C371, C372 and C373 with 0.01uF caps. It's convenient to just move these ground capacitors over to the empty spots. Sony BA-4D chassis remove and move caps

YPbPr wiring on the chassis BA-4 chassis - KV-27V40 YPbPr mod

To provide greater clarity, the following image illustrates the correct connections for the wires. This image was sourced from the Sony KV-27S42, but the concept remains consistent. Sony BA-4D YPbPr, blanking and ground

STEP 8: 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?

Depending on your CRT, you might need to find a good place to mount the SCART port.

Sony KV-27V40 img

Holes for an unused AV jack were used for YPbPr jacks for a factory look.

Reducing interference

Sometimes you might notice micro interference in the video signals. This is expected. To reduce it, try the following.

  • Use diodes in-line for RGB signal
  • Make sure your blanking wire is connected after the diode that feeds into the chroma chip (see diagram)
  • Try routing most of the cabling below the PCB
  • Keep the ribbon cable short
  • I really didn't find any difference in interference in using shielded vs non-shileded cables. Therefore, this is optional.

Getting into the service menu

  • Turn the set on and then put into standby
  • Press the Display, 5, VOL + buttons in sequence
  • Turn on the CRT and you should be in service mode
  • Use buttons "1" and "4" on the remote control to navigate the service menu
  • Use buttons "3" and "6" to adjust the selected data

Pictures of the mod

Games (KV-27V40)

Street Fighter II img

Street Fighter II img

Street Fighter II img

Street Fighter II img


Full back img

Back label img

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