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Unknown STB “Spectradyne CH1 1.0” ISA Cirrus Logic GD5426 card with S‑Video/COAX – any info?

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First post, by Linoleum

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Hi everyone,

I recently picked up an unusual ISA VGA card and I’m hoping someone here might recognize it or have documentation, drivers, or background info. Card details:
- Manufacturer: STB Systems
- Silkscreen name: SPECTRADYNE CH1 1.0
- PCB marking: 1X0‑0228‑402
- Copyright: (C) 1993 STB Systems Inc.
- Chipset: Cirrus Logic CL‑GD5426‑80QC‑A
- Outputs: VGA, S‑Video, COAX
- Assembly date: 26/94 (Mexico)
- BIOS is attached (and mentions STB NTSC VGA rev2.06... and IBM... and AWARD!?!)

Here’s a photo of the card (you might have seen it floating on eBay):

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The attachment IMG_6605.jpeg is no longer available

What I’ve discovered so far:
- The S‑Video output works perfectly under DOS (tested DOS prompt, Doom, Wolf3d, Links386).
- The VGA output goes mostly blank after TV‑out is activated — sometimes I only get a blinking cursor at the top of the screen, which looks like the card is switching to 15 kHz TV timing.
- The card is correctly identified (CL‑GD5426) by NSSI and univbe.

Interestingly, SVIDEO works most of the time, but I've seen one exception: when displaying the PCX splashscreen image when launching Direct Access 5. When this happens, this is the only time the VGA image comes up and shows the previous mode 80 image (in this case the menu itself). Very weird... But it proves the VGA output works!

What I’m looking for
- Any documentation, or OEM manuals mentioning Spectradyne CH1
- STB driver disks that might include TV‑out utilities
- Information about whether this card supports VGA + TV simultaneously, or only one output at a time
- Any historical context about this specific STB multimedia line

If anyone has seen this card before or has old STB OEM driver floppies lying around, I’d love to hear from you. This seems to be a pretty obscure piece of early‑90s multimedia hardware.

Thanks!

P3 866, V3, SB Audigy2
P2 400, TNT, V2, SB Audigy2 ZS
P233 MMX, Mystique220, V1, AWE64
P166, S3 Virge, SB32, PicoGus
486DX4 100, CLGD5424, SB32
Prolinea 4/50, ET4000, SB16
SC386SX 25, TVGA8900D, Audician32
286 10, ATI VGA, Forte16
PS2 30/286, SBP

Reply 1 of 3, by mkarcher

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The Cirrus chip only has one video output, so it can not produce two images at different scan rates (like VGA at 31.5 kHz and NTSC video at 15.7 kHz). So I expect it is physically impossible for that card to output correct VGA and TV images at the same time. Some things I observed on that card: U4 is a Sony chip, likely an RGB-to-NTSC encoder. U1/U2/U3 are analog amplifiers, I suppose for luma, chroma and composite. The EEPROM XLS93LC46 and the 16-position encoder are not present on standard ISA Cirrus cards, so they are probably something that is used by the NTSC BIOS. And last, but not least, the chip might run into performance issues because only 16 bit of its 32-bit RAM bus is populated. While ISA might prove to be the tighter bottleneck in framebuffer operation most of the time, the upgrade to 1MB RAM (by populating the other 4 sockets) should have a noticable effect in accelerated Windows.

Reply 2 of 3, by Linoleum

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mkarcher wrote on 2026-04-01, 08:01:

The Cirrus chip only has one video output, so it can not produce two images at different scan rates (like VGA at 31.5 kHz and NTSC video at 15.7 kHz). So I expect it is physically impossible for that card to output correct VGA and TV images at the same time. Some things I observed on that card: U4 is a Sony chip, likely an RGB-to-NTSC encoder. U1/U2/U3 are analog amplifiers, I suppose for luma, chroma and composite. The EEPROM XLS93LC46 and the 16-position encoder are not present on standard ISA Cirrus cards, so they are probably something that is used by the NTSC BIOS. And last, but not least, the chip might run into performance issues because only 16 bit of its 32-bit RAM bus is populated. While ISA might prove to be the tighter bottleneck in framebuffer operation most of the time, the upgrade to 1MB RAM (by populating the other 4 sockets) should have a noticable effect in accelerated Windows.

Yeah that single output theory makes a lot of sense...

I did upgrade the card to 1mb... But, anyways the 386sx it is sitting in has a far greater chance to be the bottleneck than this card has.

P3 866, V3, SB Audigy2
P2 400, TNT, V2, SB Audigy2 ZS
P233 MMX, Mystique220, V1, AWE64
P166, S3 Virge, SB32, PicoGus
486DX4 100, CLGD5424, SB32
Prolinea 4/50, ET4000, SB16
SC386SX 25, TVGA8900D, Audician32
286 10, ATI VGA, Forte16
PS2 30/286, SBP

Reply 3 of 3, by Linoleum

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Mystery has been solved by a VCFED user: https://forum.vcfed.org/index.php?threads/loo … 6/#post-1496898

It's a TV out card that was used in hotel movie rental systems!! 🤣!

P3 866, V3, SB Audigy2
P2 400, TNT, V2, SB Audigy2 ZS
P233 MMX, Mystique220, V1, AWE64
P166, S3 Virge, SB32, PicoGus
486DX4 100, CLGD5424, SB32
Prolinea 4/50, ET4000, SB16
SC386SX 25, TVGA8900D, Audician32
286 10, ATI VGA, Forte16
PS2 30/286, SBP

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