BKM 68X alternative input board

What is this?

The original Sony BKM-68X is the RGB and YPbPr input card for Sony's BVM-A series professional monitors. Original cards regularly sell for $500 to $1,000 or more, when you can find them at all. This open-source alternative, designed by Martin Hejnfelt (immerhax.com), gives you the same functionality at a fraction of the cost. Simply plug your retro consoles in via BNC and get a clean RGB or component video signal into your BVM-A monitor.

The board buffers and level-conditions your signal, then passes it straight through to the monitor. There is no aperture circuit and no additional processing. What you put in is what you see on screen.

Compatible Monitors

This board is compatible with the Sony BVM-A14F5, BVM-A20F1, BVM-A24E1W, and BVM-A32E1W in all M, U, and A variants. It installs in any OPT slot.

Choose Your Version

Rev E (8 BNC)

The Rev E has eight BNC connectors. It provides RGB or YPbPr input and loop-out across three channels, plus an external sync input and loop-out. Each input channel has a switch to select 75Ω termination or passthrough for daisy-chaining to another monitor.

Rev F5 (10 BNC)

The Rev F5 has ten BNC connectors. It includes everything found in the Rev E, plus dedicated HSYNC and VSYNC inputs with loop-out. If you are working with sources that output separate H and V sync signals, such as certain arcade boards, PCs, or consoles in progressive modes, this version has you covered without any adapters or sync combiners.

What signals does it accept?

The board accepts RGB (with CSYNC, sync-on-luma, or composite video sync) and YPbPr component video at resolutions ranging from 240p through 1080i. The onboard sync separator handles polarity detection automatically. For best results, CSYNC at 75Ω levels is recommended.

Better sync handling than the original

This board actually handles sync better than Sony's original BKM-68X. Consoles and sources that give the OEM card trouble, especially those with non-standard refresh rates or noisy sync signals, work reliably here. Even MiSTer FPGA cores that are famously problematic on the original 68X display a stable picture on this board. DoDonPachi, for example, runs at a non-standard 57.6Hz VSYNC that causes the original card to scroll the picture, while this board holds it steady.

Tested and verified with

This board has been tested and verified with a wide range of consoles and sources, including the SNES (1CHIP and 2CHIP, US and EU, CSYNC and sync-on-luma), Genesis and Mega Drive (models 1 and 2, CSYNC and CVBS sync), Master System (standalone and via Power Base Converter), Nintendo 64 (RGB modded, CSYNC), PSone (CSYNC), PS2 (RGBS, RGsB, and YPbPr up to 480p), PS3 (YPbPr up to 1080i), Wii (YPbPr at 480i, 480p, and 576i), Xbox 360 (YPbPr up to 1080i), PC Engine (external RGB mod, CSYNC), Analogue Nt Mini (RGBS), Amiga 500 (RGBS, PAL), and MiSTer FPGA including notoriously tricky cores.

Under the hood

Video signals are buffered through a THS7374 with the low-pass filter disabled and switched via ADG1611 analog switches. Sync is separated by an ISL59885 with a front-end color trap filter for clean extraction even from noisy composite video sync sources. The Y/G channel includes an ISL4089 sync-stripping circuit that activates automatically for YPbPr and sync-on-green signals to prevent overbrightness. The FPGA handles sync polarity detection and communicates with the BVM-A backplane, replicating the original BKM-68X electrical interface. All active inputs feature 75Ω termination switches.

This is open-source hardware released under the
CERN Open Hardware Licence v2 (CERN-OHL-W).

Design files are available at github.com/skumlos/bkm-68x-simple.
Designed by Martin Hejnfelt at immerhax.com.