Sony KV (BA-4D) RGB

SuntharAbout 6 min

Sony BA-4D chassis CRT RGB mod

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

This is a fairly straightforward mod to perform. For CRTs that are larger than 20", it is recommended you use shielded RGB cables internally.

Below mod was performed on a Sony KV-20S90, by a reddit user /u/atomized69. I also performed a similar mod on KV-20S42. Instructions below should also apply to these models:

KV-13M42
KV-20M42
KV-20S42
KV-20S43
KV-20S90
KV-27S42
KV-27V42
KV-27S46
KV-27S66
KV-35S36

Also, checkout this latest KV-20S42 RGB mod tutorial as well.

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.

READ THIS BEFORE CONTINUING

Plan of attack

READ THIS TO PREPARE

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.

READ THE RGB MODDING THEORY

Service manuals

Specs

Sony KV-20S90

Manufactured: October 2001, Mexico
NTSC, 60 Hz - 95W
Chassis: BA-4D
Tube: A51LDG51X
Jungle Chip: CXA2133BS
OSD Chip: M37273MF-255SP

Sony KV-20S42

Manufactured: September 1999, Mexico
NTSC, 60 Hz - 90W
Chassis: BA-4D
Tube: A51LDG550X
Jungle Chip: CXA2061S
OSD Chip: M37273MF-255SP

Sony KV-27S42

Manufactured: September 1999, Mexico
NTSC, 60 Hz - 90W
Chassis: BA-4D
Tube: A68LML50X
Jungle Chip: CXA2133BS
OSD Chip: M37273MF-255SP

Schematics

Sony BA-4D chassis schematics

Mux diagram

If you are building your own circuit, this diagram should help. The diagram is for KV-27S42, it will also work for KV-20S90, KV-20S42 or any other BA-4D chassis.

Sony BA-4D 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.

Degauss wire
Power wire
Ground wire attached to the neck board
Yoke deflection coil wire
Anode wire (this is the one with the rubber cap)
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.

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.

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: Add RGB inline diodes (optional, but recommended)

To reduce interference, it is recommended to add these inline diodes. You will be lifting one side of the R025, R026, R027 and add diodes.

KV-27V40 - Heat shrink was used in the middle one to avoid shorts. BA-4 chassis - KV-27V40 RGB mod

KV-27V42 - Heat shrink was used in the middle one to avoid shorts. BA-4 chassis - KV-27V42 RGB mod

KV-27S42 - Below picture shows before adding the diodes. BA-4D chassis - KV-27S42 RGB mod

KV-27S42 - After adding diodes inline BA-4D chassis - KV-27S42 RGB mod

Pay attention to the diode direction and how it was installed. This is extremely important. Otherwise, OSD will not work.

Also, adding didoes means you will need to use 1KΩ resistors on the RGB mux board.

STEP 3: 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 Brown wire here is used for blanking

KV-20S42 - RGB/Blanking wiring BA-4D chassis - Full RGB mod

KV-27S42 - RGB/Blanking wiring BA-4D chassis - KV-27S42 RGB mod

STEP 4: Connect Sync, Audio and Ground

Wire colors

Black wires is common ground
Grey wire is for right audio
White wire is for left audio
Orange and purple wires are auxillary. Seen either grounded or tied away for future use.
Yellow wire is for sync

KV-20S42 - Sync, Audio and Ground

KV-27S42 - Sync, Audio and Ground S-Video detect was permanently grounded to enable sync through luma. See the orange wire that goes from S-Video detect to ground. This disables the specific composite input that is attached along side S-Video. Other composite inputs should continue to work.

KV-20S90 - Sync, Audio and Ground BA-4D chassis - Full RGB mod

Tips

Later BA-4D 27" sets use a sync separator IC (IC010) for switching to the S-Video input, rather than the logic signal on the shield pins used in previous models. If the IC fails to properly recognize the signal, it loses sync. When I attempted to input RGBs from a Dreamcast with a DC2VGA DIY adapter in CSYNC mode to a KV-27V42 that I modded for a friend, it wouldn't sync unless I changed the ID-1 value to "23." This setting change reverts S-Video detection to the shield logic method instead of the sync separator method. You might want to try changing that setting to see if it resolves your issue.

On KV-27S66 service menu ID1 setting had to be changed from 155 to 23 in order for the s-video ground sensing to actually take effect.

STEP 5: 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 Model	KV-20S40	KV-20S90	KV-20S42	KV-27S42
CRT inline resistors	5.6kΩ	5.6kΩ	5.6kΩ	5.6kΩ
Add diodes to RGB inline?	Yes	Yes	Yes	Yes
Add diodes to blanking on chassis?	No	No	No	No

RGB termination (R1, R2, R3)	75Ω	75Ω	75Ω	75Ω
RGB inline resistors (R4, R5, R6)	1kΩ	1kΩ	1kΩ	1kΩ
Audio LR (R7, R8)	1kΩ	1kΩ	1kΩ	1kΩ
Diode (R9)	1N4148	1N4148	1N4148	1N4148
Open (R10	--	--	--	--
Blanking Resistor (R11)	1kΩ	1kΩ	1kΩ	1kΩ
Add diodes to RGB lines	Yes	Yes	Yes	Yes

STEP 6: 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-20S42

Sony KV-20S90

Sony KV-27S42

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.