A DIY Test Generator...
 

From an old DOS computer. Besides that you will need a VGA card, a scan converter (from VGA to NTSC) and two downloads.
Download showjpg from here: http://www.pictview.com/showjpg.htm
And download PM5544.jpg from wikipedia.
Set up your autoexec.bat so that it will go into the program upon bootup. Then disable your keyboard in BIOS and disconnect it.
Most test generators these days are software driven rather than hardwired circuitry.
Scan converters can be either internal or external. Some VGA cards have an NTSC output.
The Chinese have a scan converter on Ebay for ~$10 (VGA2AV).

There's also DTV converter boxes that can play pictures off USB stick. Heck most XP to Windows 7 era graphics cards in laptops and desktops have S-Video output.

The purpose of this thread is to re-use an old DOS computer into something useful.
Do those DTV converter boxes go right to the pattern without any human intervention upon power-up?
Anything with S-video output would have to be converted to use as a composite video source.

Wow, that's a huge video card, and it's only 8 bit ISA!
A $5 Raspberry Pi Zero could do the same with native composite output.
S-Video can be converted to composite by crossing both Luma and Chroma wires.

I like it. The only problem ss these days is that a computer like that AST pictured above sells for likely more than what you'd pay for a Sencore VG91 and certainly more than a B&K 1076.

The last while I have been using one of those cheapo china deluxe android TV boxes that outputs NTSC and I done a few test patterns in high resolution 4:3 MP4 format.

That big ISA board is actually a scan converter board. You need a VGA card to drive it.
Do you still not have your old DOS computer laying around?
I find computers on the roadside every 6 months or so. Usually they will have a bad battery or an HD filled up with crap or a bad PS. And the owner just went out and bought a new one.
I'll check into that $5 Raspberry Pi Zero.
Edit: Didn't see any raspberry pie zeroes on Ebay for $5.

I haven't seen a dos era computer available in 15 years.
I can't stand anything older than XP so even if I found one I wouldn't buy it/take it off the curb.

It's not a bad project if you have the stuff laying around, but at this point the only people who do are computer collectors, and old folks who never let things go....And maybe a few abandoned business buildings.

My bad, they're actually $10 at this moment. You can find authorized resellers here:
https://www.raspberrypi.com/products/raspberry-pi-zero/
There's a header for composite output, you just have to solder a connector to it.
On the software side you need to edit a config file. Many analog video standards are supported. I use NTSC-J for deeper blacks.
https://www.raspberrypi.com/document...#video-options

I own two 386en and a Socket 7 PC I built from parts.
https://studioraichu.net/materials.html

It's probably got malware baked into ROM. https://youtu.be/Epp-8n-_CWA&t=347

Thanks for the info. I researched the Raspberry Pi and there is quite a bit of info out there. Sure solves the problem of a hard drive spinning all the time and it's a lot smaller.
Don't know if you've noticed but Ebay now has a disclaimer about "import fees".
NTSC-J, I have a Tektronix TSG170 that has one of the two bar patterns set up for zero black. It was the Japanese version generator. I got it for a dollar off Ebay so I can't complain. And it doesn't affect the other patterns. Thanks again.

lol. That's my thoughts exactly when I bought it. The one I got is about 10 years old now. It has never seen internet access and never will. As a video player for NTSC it works great and can scale the screen for perfect 4:3 video.

My only complaints with is outside of the possiblility of sketchy malware is the crappy USB ports and the RF interference it puts out. It will totally null out everything on the AM brodcast band 50 feet away.