Connecting A 15 kHz CRT Monitor To A Modern PC

Note: I frequently get asked about how to connect a 15 kHz1 CRT monitor to a modern PC so I’ve decided to summarize my learnings here and refer this document to anybody wondering how it can be done. It will be updated as I learn more. Feel free to reach out to me if anything is unclear.

CRT Monitor

The easiest and most safe way to output a 15 kHz signal to a CRT monitor is to use a source that outputs it natively. This format was widely used by both computers, arcade systems and video game consoles but has since been replaced by higher resolutions. Fortunately there are still several ways to connect your modern PC to a CRT monitor.

Output

The first step is to configure the output from your PC to be within the 15 kHz specification. This can be done via hardware, software or a combination of both.

Note: These methods have been tested on the Windows operating system. I’m sure they can adapted for use with other operating systems but your mileage may vary. I recommend using Windows XP or Windows 7.

ArcadeVGA

The easiest way is to use an ArcadeVGA, a purpose built GPU that is capped to 15 kHz unless you enable thee 25 kHz multi-frequency monitor mode. It is safe to use from POST2 to gameplay and is your safest bet as a plug-and-play solution.

CRT_Emudriver + ATOM-15

Another option is to use an older AMD/ATI GPU with CRT_Emudriver, a modded version of the Catalyst software (now AMD Radeon Software Crimson) that enables the use of magic resolutions3 and super resolutions4 within the 15 kHz specification.

Warning: Only using CRT_Emudriver can damage your CRT monitor if it’s powered on before the driver is loaded as your GPU will still output resolutions higher than those within the scope of the 15 kHz specification.

To heed the warning above you can (on top of using CRT_Emudriver) flash your GPU with ATOM-15. It’s a modified BIOS firmware that allows you to specify what video modes can be displayed using the GPU. Depending on your CRT monitor you can cap the output to 15, 25 or 31 kHz and POST safely as if you were using an ArcadeVGA card.

NVIDIA Control Panel

If you have an NVIDIA GPU is is possible to use the NVIDIA Control Panel to force the output to 15 kHz. To do this you must select your CRT monitor from the list of connected displays and add a Custom Resolution.

Setting Value
Horizontal pixels 320
Vertical pixels 240
Refresh rate 60 Hz
Scan type Progressive
Color depth 32 bpp
Timing CVT



It should look something like this:

Custom resolution

You might have to tweak these values or adjust the geometry of your CRT monitor.

Warning: This method is also unsafe if the CRT monitor is powered on and the custom resolution is not applied.

Connection

Once your GPU is outputting 15 kHz it needs to be connected to your CRT monitor. There are several ways to do this.

RGBHV

If your CRT monitor supports RGBHV5 you should be able to use a VGA to RGBHV BNC cable. These are fairly common and a simple way to connect your GPU to a CRT monitor. You might have to use a DVI to VGA adapter if your GPU doesn’t have a VGA port.

RGB Interface

Many CRT monitors only support RGBS6. To combine the sync you cound get a sync combiner but I prefer using an RGB interface. I recommend the Extron RGB interfaces as they are of very high quality and affordable. The particular model I’m using is an Extron RGB 192.

Y/C (S-Video)

If you’re CRT monitor and GPU both support S-Video this is likely going to be the easiest and cheapest way of connecting them. The video quality won’t be as good as RGB but it might be good enough for a lot of people so I thought I’d mention it.

JPAC

If the CRT monitor you are connecting to your PC is part of an arcade system using the JAMMA standard you might want to get a JPAC. It takes VGA input and pipes the video as if it was output from a JAMMA board.

Closing Words

Sometimes it’s not possible to output 15 kHz and if that’s the case you may still be able to connect your PC (or other device) to your monitor via downscaling. I’ve had issues with downscaling but I recommend giving Fudoh’s write-up a read.

Enjoy beautiful analog video.


1: 15 kHz is commonly referred to as 240p.
2: Power-on Self Test, the routine that happens before your OS starts loading.
3: Atrociously wide resolutions used to trick Hyperspin from crashing. (?)
4: Upscaled resolutions.
5: RGB with separate horizontal and vertical sync. VGA uses this type of RGB signal.
6: RGB with combined horizontal and vertical sync.