Sony (BA-4D) KV-27S42 RGB

# Sony (BA-4D) KV-27S42 CRT RGB mod

The Sony KV-27S42 is a retro 27" display, launched in 1999, known for its exceptional image quality and versatility. Featuring the acclaimed Sony Trinitron A68LML50X tube, this model offers a vibrant viewing experience with an aspect ratio of 4:3, making it ideal for classic gaming and retro content.

This CRT is equipped with multiple input options, including Composite, S-Video, and RF. For enthusiasts, the KV-27S42 is modifiable for RGB input using the recommended Sunthar mux board, enhancing its compatibility with several retro gaming consoles.

Sony KV-27S42 remains a sought-after model for those appreciating the nostalgia of CRT technology.

View full CRT details and more mod examples →open in new window

This advanced mod tutorial is divided into three chapters, focusing on advanced modifications to address previous challenges:

• Chapter 1: Addresses key challenges like requiring a dummy plug for stereo audio and a dummy S-Video plug to activate S-Video by grounding the detect pin.
• Chapter 2: Explores how to use a remote control to seamlessly switch between RGB, composite, and component inputs.
• Chapter 3: Demonstrates how to utilize an external blanking signal, including lower-voltage signals from MiSTer, to switch inputs automatically. This allows all stock inputs to remain functional without requiring physical switches.

Chapter 2 & 3 is in progress.

# Table of Contents

# Contributors

Thank you to everyone who contributed to this guide:

• Aaron’s Retro Basementopen in new window — showcase author
• Nostalgia FX Workshopopen in new window — showcase author
• ALttNopen in new window — showcase author

# CRT safety

READ THIS BEFORE CONTINUING

# Plan of attack

READ THIS TO PREPARE

# Manuals and Datasheets

• Sony KV-27S42 Service Manualopen in new window
• KV-27S42_SMopen in new window
• KV-27S42_UMopen in new window
• Mitsubishi M37273MF-255SP Datasheet (OSD) — Available for Pro Users only. See CRT detailsopen in new window for access.

# Specs

• Manufactured: Mexico (1999)
• Format: NTSC
• Chassis: BA-4D
• Tube: Sony Trinitron A68LML50X
• Jungle Chip: Sony CXA2133AS
• OSD Chip: Mitsubishi M37273MF-255SP
• Screen Size: 27"
• Inputs: Composite, S-Video, RF

# Schematics

# RGB mux diagram

Prepare the mux diagram. If you are building your own circuit, this diagram should help.

# Chapter 1: No more dummy plug needed

We'll be using the diagram below for this modification. While it’s specifically designed for the KV-27S42, it is also compatible with the KV-27V42 and other 27" BA-4D chassis models that use luma for sync. However, this method does not apply to 20" or smaller BA-4D models, as they do not require luma for sync.

RGB Mux Calculatoropen in new window

# STEP 1: Remove RGB ground resistors

First we will remove the following components. So, nothing new here.

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.

• R086 (680Ω) Red ground resistor
• R087 (680Ω) Green ground resistor
• R088 (680Ω) Blue ground resistor

# STEP 2: Add RGB inline diodes

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.

Pay attention to what side the diode is added and the direction of the diode stripe.

# STEP 3: Attach R, G, B and blanking wires

Ensure that the R, G, B, and blanking wires are connected as shown in the picture.

# STEP 4: Permanently enable stereo

Permanently enabling stereo can be a bit tricky, especially if you're using Video 1 input sync for RGB. Here are your options:

• Option 1 (Recommended): Simply insert a plug into the red RCA port. This is the easiest and most effective method.
• Option 2 (Not Recommended): Cut the trace to force stereo. However, this isn't as simple as a single cut—you'll need to cut the trace from both sides and then resolder the right audio connection back into the circuit.
• Option 3 (High Effort, Cleanest Solution): If you have a desoldering tool, you can remove the physical clip that forces mono when nothing is plugged into the red RCA port. This is the most involved method but results in a clean and permanent solution.

Below, you'll find pictures demonstrating Option 3.

# STEP 5: Connect sync and s-video detect

Finally, we have a purpose for the orange wire! In other mods, you may have seen it labeled as auxiliary or simply grounded as unused.

• Yellow wire: Used for sync.
• Orange wire: Functions as S-Video detect, automatically grounding when a blanking signal is detected from the SCART input.

# STEP 6: Audio and ground wires

Now wire the audio wires.

Final full mod picture.

# STEP 7: Introducing the MUX 1.4B board.

Latest v1.4B board packs some useful features:

1. Automatic S-Video Detection – Uses a PN2222A transistor to handle S-Video detection, eliminating the need for a dummy S-Video plug, which was a hassle.
2. Auxiliary RGB Port – Adds an additional RGB input, allowing for an extra SCART or 8-pin mini DIN connection.

The board is the same size as the 1.3B/1.3C models.

# STEP 8: Build your MUX board

This 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 mux calculatoropen in new window to play with your own values.

Compatible mux boards:

• RGB MUX BOARD KIT 1.4Copen in new window
• RGB MUX BOARD KIT 1.4Bopen in new window

Buy your RGB mux board kit

You can connect a second XRGB input using the auxiliary input through a 10-pin IDC connector on this board.

# Sync issues

Some Sony KV-27S42 CRT televisions may exhibit sync issues with certain consoles, including the Raspberry Pi, Nintendo 64, and Super Nintendo. This issue is typically found on later KV-27S42 revisions that use a specific sync-separation IC.

A workaround is to disable the sync-separation IC by changing the ID-1 value in the service menu from 145 to 23.

Credit goes to Kaz Packman for discovering this solution.

# Additional Pictures

I had my boards loose during testing. Be extremely careful to avoid applying pressure on the chassis or accidentally touching the power board.

# Pictures

# Mod Photos

Sony KV-27S42 RGB Mod. LMUX BOARD.

# Photos by Nostalgia FX Workshopopen in new window

# Photos by ALttNopen in new window

This Sony KV-27S42 CRT experienced sync issues with N64 and SNES. This was a later model KV-27S42, that used a specific IC for sync separation. This was disabled by changing the ID-1 value. Thanks to Kaz Packman for finding this solution.

# Reference Photos

See more photos and contributions →open in new window