The manual

What to buy

You need a PC with a leasable graphics output, a converter that passes the required timings to analogue RGB, and a 15 kHz television with RGB input.

Check the PC first. Then choose the converter and the television connection together.

PC requirements

Use an AMD card with the amdgpu driver for the documented setup. The kernel handles leasing and modelines. Nvidia’s proprietary driver does not expose leasable connectors in this setup. Intel has not been tested here; there are also no reported failures to confirm its behaviour.

The desktop compositor must support DRM leasing through wp_drm_lease_v1. Hyprland is the supported and tested compositor. It lends the television connector to OmaCRT instead of managing it as another desktop monitor.

The system needs systemd and a mounted debugfs. A boot-time service writes to the kernel debug interface to mark the television connector as non-desktop before Hyprland starts.

Run omacrt doctor before buying hardware. With no converter connected, it checks:

• which driver the card is on
• whether the compositor will lend out a connector, and which one
• whether systemd is there
• whether debugfs is mounted

Resolve any failed prerequisite before choosing a converter.

The converter

Choose a converter that accepts the graphics card’s timings and outputs analogue RGB. A fixed-resolution scaler cannot preserve the different line counts used by the games.

The converter describes the RGB-Pi 2 used for development and its sync requirements. The main connection options are:

The fixed-mode option can produce a picture, but it uses one output resolution and refresh rate for every console.

Reflex Prism: untested alternative

The following alternative has not been tested with OmaCRT. Check its connections and capabilities with the seller before buying.

The Reflex Prism from MiSTer Addons was listed at eighty dollars when this guide was written. Its published description specifies lag-free one-to-one conversion to RGB, component and S-Video, without downscaling. Passing through the input timing is the capability OmaCRT needs.

It should use the same wide modeline, leased connector and software. The differences to check are sync, audio, power and display identification.

From version 1.05, the Prism combines sync internally. This should remove the external sync adapter and the RGB-Pi 2 control-bus configuration described in The converter. The RGB-Pi 2 lock-monitoring workaround is specific to that board.

The Prism provides video on HD15 and a Saturn-style Mini-DIN, plus audio on a 3.5 mm jack. The material consulted for this guide does not establish whether the Mini-DIN also carries audio. Ask the seller:

Does the Mini-DIN output carry the audio pins as well as RGB and sync, or is audio only on the 3.5 mm jack?

If the Mini-DIN carries audio, use a Saturn-to-SCART RGB cable with audio. If audio is available only on the jack, use an RGB, VGA or HD15-to-SCART adapter with phono audio inputs, plus a 3.5 mm-to-twin-phono lead. This connects stereo audio to SCART pins 2 and 6 alongside the video. Two separate SCART plugs cannot combine those signals into one input.

OmaCRT sends audio through the graphics card’s HDMI output. The kernel exposes that output only when the connected device’s identification advertises audio support. Check this row in omacrt doctor:

OK   EDID advertises audio        HDMI audio pin available

If this check passes, audio travels with video over HDMI and leaves through the converter’s audio output. Otherwise, route the PC’s headphone output to the SCART adapter’s audio inputs. The Prism’s HDMI audio advertisement has not been verified here; it needs a test with omacrt doctor.

No Prism was available for testing when this guide was written, and availability has been limited. The description above is based on published specifications and OmaCRT’s signal requirements. Also ask whether it needs an external power supply. The RGB-Pi 2 used here takes power from HDMI’s five-volt pin.

From version 1.1, the Prism offers browser-based configuration of its display identification. Ask whether it accepts an arbitrary 256-byte identification binary, including a custom extension block with a vendor-specific section. If so, it may be possible to store the non-desktop marker on the device itself. That could remove the boot service, kernel override and reboot requirement. This has not been confirmed.

Lower-cost VGA converters

An HDMI-to-VGA converter with a Lontium chip is a lower-cost option. The prices recorded for this guide were five to twenty euro for the converter, or twenty-five to fifty euro with a passive sync combiner. This path has no audio.

RetroRGB notes that inexpensive converters can change internally without a change to the listing. Confirm the chip and capabilities of the unit you will receive.

Converters and cables to avoid

Check products sold as “HDMI to SCART converters” carefully. Many are scalers with fixed 576i output. They can show a picture but cannot preserve each console’s line count. Look for explicit support for passing through input timings.

On a VGA path, avoid adapters with slow microcontrollers that lose sync during timing changes. MiSTer-specific cables also use different signal requirements: 3.3 to 5 V on pin 9 and TTL composite sync on pin 13. They do not provide the required sync in this setup.

Avoid a bare passive VGA-to-SCART cable. It does not provide the required sync conditioning; poor shielding and weak sync can also cause problems. Use a suitable sync combiner or adapter.

The television

Choose a 15 kHz television or monitor with RGB input, PAL or NTSC. This can be a portable set, a Trinitron, a broadcast monitor or a European television with RGB-capable SCART. Check the actual input specification: a component socket alone does not establish RGB support. Composite and S-Video reduce image detail compared with RGB.

A standard VGA monitor is unsuitable for this signal. Its minimum horizontal frequency is roughly twice 15 kHz. Adding a SCART adapter does not change the monitor’s scan-rate limits.

RGB-capable SCART carries video, blanking and audio in one plug. Check that the converter drives the blanking pin; otherwise the television may show a black-and-white picture. An older set may need time to warm up before its geometry settles. After long storage, an older set may need about an hour for its geometry to settle.

What it does not need

The progressive-output setup does not require the following extras:

A patched kernel is unnecessary for progressive output. Interlace needs patches and remains disabled in the documented setup. The 480-line systems use 240p instead.

A scaler, line doubler, upscaler or OSSC is unnecessary. Those devices adapt 15 kHz video for modern displays; this setup sends it to the CRT directly.

CRT shader effects are unnecessary on the television. Its phosphor mask, scanlines and glow are already part of the display.

Omarchy is optional. The launcher, display process and command line require Hyprland. Omarchy adds the bar widget, panel, library overlay, Television menu entry and desktop theme integration. See On the desktop for details.

Before buying

1. Run omacrt doctor and resolve problems with the driver, compositor or kernel interfaces.
2. Choose a converter that supports the timings and connections you need.
3. If you need a television, choose one with a compatible 15 kHz input.