The Multibridge came with a specific half-length PCIe host card for your desktop PC. These cards have capacitors that degrade. If the host card has no blinking LEDs, replace it. You can sometimes use a generic PCIe Redriver card, but success is low.
A failed firmware update could sometimes "brick" the unit. The solution often involved shutting down the computer, connecting the unit via USB only (not PCIe), powering it on, and then running the firmware update utility again. blackmagic multibridge utility
: Operating as a high-quality A/D or D/A converter without a host computer connection. Technical Specifications & Compatibility The Multibridge came with a specific half-length PCIe
Do not look in the modern Desktop Video software for initial setup. You can sometimes use a generic PCIe Redriver
This is the biggest pain point for users today:
The Blackmagic Multibridge Utility is Intel-only (x86) . It does not run natively on Apple Silicon. You must run macOS via Rosetta 2, and even then, PCIe tunneling over Thunderbolt on Apple Silicon is notoriously unstable for this legacy hardware.