HKTV13RGB — RGB Mod for the Emerson HKTV13 "Hello Kitty" CRT TV

An open-hardware RGB injection board that adds clean, switchable RGB input to the Emerson HKTV13 Hello Kitty CRT television. The module is an interposer that sits between the TV's neck board and main board, in line with the existing 7-pin OSD link. It either passes the original OSD signals straight through, or pulls them out and injects external RGB in their place — letting you feed RGB from a retro console, scaler, or other source while keeping the set's original on-screen display (OSD) fully usable.

⚠️ High-voltage warning. CRT televisions contain lethal voltages that can remain present even when unplugged. The CRT anode and the chassis around it can hold a dangerous charge for a long time. Do not attempt this mod unless you understand how to safely discharge and work inside a CRT. You perform this modification entirely at your own risk.

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Table of Contents

• What it does
• How it works
• Gallery
• Repository contents
• The board
  • Connectors & pinout
  • Bill of materials
• Ordering the PCB
• Installation
• Bypass / reversibility
• Setup & adjustment
• Troubleshooting
• License
• Credits

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What it does

Unusually, the HKTV13 has two OSD generators — one of them lives on the neck board and sends its OSD to the main board (the jungle/tube-driver chip) over a 7-pin connector (P502). Because of that dual-OSD design, the TV already has its own internal, buffered switching circuit between the two OSD sources, and there is no clean point to mux external RGB into it.

This mod takes a different approach. It inserts itself into the neck-board OSD link as an interposer and switches the whole path out rather than muxing:

• It taps the neck-board OSD line and runs its own THS7376 video amplifier straight into the jungle chip — the same way other RGB mods drive a tube driver.
• An external analog RGB signal comes in (via RCA/coax or SCART) and is buffered by the same amplifier.
• A TS5V330 analog switch selects between (a) the TV's original OSD + normal signal path, or (b) the external RGB — switching the circuit over entirely instead of blending the two OSD circuits.

The result is a sharp RGB picture on the original Hello Kitty CRT, with the stock OSD/normal signal fully restored when you switch back. Because the board sits in the existing signal path with the same 7-pin pinout on both sides, it can be bypassed by simply unplugging it and reconnecting the neck board to the main board directly (see Bypass / reversibility).

The external RGB harness is wired compatible with the Sunthar / "Sunthar-style" RGB pinout, so existing SCART/RGB cables built to that convention will work.

How it works

Block	Part	Role
Video amplifier	THS7376	Buffers/level-shifts the RGB and drives it into the jungle chip.
Path switch	TS5V330 analog switch	Switches the whole path between the original OSD/normal signal and external RGB.
Power regulator	AMS1117-5.0 LDO	Provides 5 V (VCC) for the board from the TV's OSD_10v rail.
Blanking gate	JP1 + R10 + LL4148	Conditions the Fast Blanking signal that drives the switch.

Fast Blanking can be sourced externally (e.g. SCART pin 16, for sources that drive their own blanking) or internally via the on-board switch — useful for sources that don't supply F_BLK. Each RGB input is terminated at 75 Ω and AC-coupled (100 nF) on the way in, then re-biased after the amplifier. The full schematic is in images/schematic.png (PDF: images/schematic.pdf) and the editable source is in the KiCad/ folder.

Gallery

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Repository contents

HKTV13RGB/
├── KiCad/
│   ├── HKTV13RGB.kicad_pro       # KiCad 9 project
│   ├── HKTV13RGB.kicad_sch       # Schematic
│   ├── HKTV13RGB.kicad_pcb       # PCB layout
│   ├── Project Symbols.kicad_sym # Custom symbols
│   └── Gerbers/
│       ├── HKTV13RGB v1.0.zip    # Ready-to-order fabrication package
│       └── *.gbr / *.drl         # Individual Gerber + drill files
├── images/                       # Build & install photos, schematic
├── LICENSE                       # CERN-OHL-S v2
└── README.md

The board

• Designed in KiCad 9.0.
• Two-layer PCB with ground via stitching.
• All RGB paths impedance-terminated; path switching handled on-board.

To open the design, install KiCad (9.0 or newer) and open KiCad/HKTV13RGB.kicad_pro.

Connectors & pinout

Pin numbering is taken from the schematic in images/schematic.png. Confirm against your board silkscreen before wiring.

J4 — Main I/O (2×5 header)

Pin	Signal	Pin	Signal
1	F_BLK (Fast Blanking in)	2	R_IN
3	SWITCH	4	C_SYNC
5	G_IN	6	B_IN
7	GND	8	AUDIO_R
9	AUDIO_L	10	GND

J1 — "OSD" (from the neck board) — silkscreened OSD. Carries the original secondary OSD signals coming off the neck board. A 7-pin 2.54 mm JST socket is soldered here so the neck-board cable plugs straight in.

Pin	Signal
1	OSD_FBLK
2	OSD_VCC
3	OSD_10v (board power source)
4	OSD_R
5	OSD_G
6	OSD_B
7	GND

J2 — "JNG" (to the main board) — silkscreened JNG. Sends the selected signal (pass-through OSD or injected RGB) on to the main board. A 7-pin wire harness is soldered to the underside here and terminates in a plug for the main board's P502.

Pin	Signal
1	DSD_FBLK
2	DSD_VCC
3	DSD_10v
4	JNG_R
5	JNG_G
6	JNG_B
7	GND

JP1 — Fast Blanking enable jumper. Gates the F_BLK signal into the OSD switch.

Test points

These pass audio and composite sync through to the main board. They are optional — not required for the RGB picture itself. In a typical install, sync for the picture is supplied by the TV's own composite input, not by the module's C_SYNC. (If you're feeding the set over SCART, you may instead pass C_SYNC / composite through here.)

TP	Signal
TP1	AUDIO_R
TP2	AUDIO_L
TP3	C_SYNC

Bill of materials

Ref	Value / Part	Notes
U1	THS7376	Video amplifier
U2	TS5V330CPWR (TSSOP-16)	Analog switch (path select)
U3	AMS1117-5.0	5 V LDO regulator
D1	LL4148	Switching diode (MiniMELF)
C1–C3	100 nF	RGB input AC coupling
C4, C5	10 µF	LDO input / output
C6, C9	1 µF	Decoupling
R1–R9	75 Ω	Video termination / series
R10	4.7 kΩ	F_BLK pull
R11	47 kΩ	F_BLK pull-down
R12	4.7 kΩ	SWITCH pull
R13, R14	1 kΩ	Audio series
R15–R17	5.1 kΩ	Bias pull-ups for the THS7376 inputs

Exact values and footprints are authoritative in the KiCad schematic.

Ordering the PCB

The fastest path is to upload the prebuilt package KiCad/Gerbers/HKTV13RGB v1.0.zip directly to any PCB fab (JLCPCB, PCBWay, OSH Park, etc.). Standard 2-layer, 1.6 mm, 1 oz copper settings are fine. The individual Gerber and drill files are alongside the zip if you'd rather supply them separately.

Installation

Take photos of every connector and wire you touch before you disconnect anything. Work on a non-conductive surface and keep one hand behind your back when the set is powered.

The mod installs in line with the existing neck-board ↔ main-board OSD link. You'll convert both ends of that link to a 7-pin 2.54 mm JST connection so the module can drop in (and out) cleanly.

1. Open the set safely. Unplug the TV, let it sit, then discharge the CRT anode to the chassis with a properly insulated tool before working near the tube.
2. Convert the neck-board cable. Replace the original 7-pin cable attached to the neck board with a 7-pin 2.54 mm-pitch JST cable. This is what will plug into the module's OSD connector (J1).
3. Convert the main-board socket. Replace P502 on the main board with a 7-pin 2.54 mm-pitch JST socket. This lets the neck board and main board connect normally again without the mod, and gives the module's JNG harness a place to plug in.
4. Prep the module connectors.
   • Solder a 7-pin JST socket to the OSD pads (J1) — the neck-board cable plugs directly here.
   • Solder a 7-pin wire harness to the underside of the JNG pads (J2) — this harness plugs into the new P502 JST socket on the main board.
5. Drop the module in line. Plug the neck-board JST cable into OSD, and plug the module's JNG harness into the main board's new P502 socket. The board is now powered from OSD_10v (regulated to 5 V on-board) and is interposed in the OSD path.
6. Bring in external RGB + audio. Wire your external RGB source to J4. The build pictured uses an external input cable wired to the Sunthar-style pinout, broken out to panel-mounted RCA/coax jacks (and/or SCART) added to the rear of the case.
7. Choose the Fast Blanking source. Set the on-board switch for external F_BLK (driven by your source, e.g. SCART pin 16) or internal F_BLK (the board supplies it) depending on your input. Set JP1 accordingly.
8. Dress and secure. Tidy and strain-relieve all wiring, double-check there are no shorts, and confirm nothing fouls the tube neck or flyback.
9. Reassemble and test (see below).

Additional reference photos of the install are in the images/ folder.

Bypass / reversibility

Because the module sits in the existing OSD link with the same 7-pin pinout on both sides, it can be removed without any further modification to the set:

1. Unplug the neck-board JST cable from the module's OSD connector.
2. Unplug the module's JNG harness from the main board's P502 socket.
3. Plug the neck-board JST cable directly into the main board's P502 socket.

The TV is now back to stock behavior. The only permanent change is the swap to JST connectors on the neck-board cable and P502 — the mod itself is fully removable.

Setup & adjustment

1. With the case still open (and observing all CRT safety precautions), power on and feed a known-good RGB signal.
2. Verify the picture switches to RGB and that the stock OSD still overlays correctly. If the OSD is missing or RGB doesn't appear, the Fast Blanking source/wiring (internal-vs-external switch, JP1, OSD_FBLK on J1, F_BLK on J4) is the first thing to check.
3. Use TP1/TP2 (audio) and TP3 (C_SYNC) to probe signals if something looks wrong. These are pass-through/optional — sync for the picture normally comes from the TV's composite input, not the module's C_SYNC.
4. Confirm sync is stable. If you're driving the set over SCART, C_SYNC / composite may be coming through the module instead — check that path in that case.

Troubleshooting

Symptom	Likely cause
No picture at all	No board power — check OSD_10v into J1 and ground; verify 5 V at the AMS1117 output.
RGB shows but OSD/menus gone	Fast Blanking not returning to OSD — check the internal/external F_BLK switch, JP1, OSD_FBLK, and F_BLK wiring.
OSD shows but no external RGB	Switch never engages — check the F_BLK source (try internal switch), SWITCH line, and RGB input wiring on J4.
Picture works only when mod removed	Re-check OSD/JNG plug orientation; confirm P502 JST pinout matches the original cable.
Weak / washed-out colors	Termination/coupling issue — verify the 75 Ω inputs and RGB ground return.
Rolling / unstable image	Sync problem — sync normally comes from the TV's composite input, so check that first; only check C_SYNC on J4 (TP3) if you're passing sync via SCART.
No audio	Check AUDIO_L / AUDIO_R on J4 (TP1/TP2) and series resistors R13/R14.

License

This project is released under the CERN Open Hardware Licence Version 2 — Strongly Reciprocal (CERN-OHL-S v2). See LICENSE for the full text. You are free to use, study, modify, and redistribute the design under its terms; derivatives must be shared under the same license.

Credits

• Design: Innov8bit / RetroLoom
• Hardware revision: 1.0 (first public release)

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This is a community modification and is not affiliated with or endorsed by Emerson or Sanrio. "Hello Kitty" and related marks are property of their respective owners.