Sony BKM-68x
The BKM-68x is an RGB / Component video input card for the Sony A-Series BVM’s. Very few were made, causing them to be extremely rare and expensive. Luckily, the board has been successfully reverse-engineered and you can buy a “homebrew version” for far less than the cost of the original, that ever performs better! More info below:
Open Source Homebrew version of the 68x:
The 68x homebrew card is currently selling for around $300, but after the global part shortage ends and cheaper versions of the FPGA are available, the card’s price will go down. The link below will always point to the newest version available.
Purchase yours here: https://retrorgb.link/68x
Martin’s blog detailing the process: https://immerhax.com/?p=624
Github: https://github.com/skumlos/bkm-68x-simple
The homebrew version of the card also doesn’t have any of the sync issues the original did, making it even better then the original in cost, performance and availability. Here’s a quick example of the fixed sync issue. More info about price and features are available in the video below and an interview with the creator is below that:
Video Overviews:
Both of these videos were shot before Martin’s homebrew card was released, but are still a decent representation of the sync issues and potential fixes..
Sync Issues / Potential fixes:
Many consoles seem to have sync issues with the 68x, as the A-Series BVM’s don’t have the “VCR Mode / Automatic Frequency Control (AFC)” that the previous BVM’s offered, which cleared up a lot of the horizontal problems. We tested different settings for the card’s configuration, as well as a lot of “tricks” to fix the sync. We’re currently working on a sync regeneration box that could potentially fix all issues with A and H series BVM’s, but at the moment, there’s no true “fix” for the 68x. Here’s some tips if you’re a current owner of the 68x:
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- Try routing your RGBs signals through a device that converts sync to RGBHV, then back through another device that converts it back to RGBs. One example might be using an LM1881-based device to convert to RGBHV, then an Extron RGB interface (203xi, 501, etc) to convert back to RGBs.
- You can run your consoles through an OSSC or RetroTINK 2x in passthrough mode, then use an HDMI to component converter. This breaks compatibility with some light gun games and Sega 3D glasses, but it’s certainly better than not being able to use it at all.
VCR Mode / AFC & Why it’s needed for the SMS:
Here’s some screenshots from the D-Series BVM manual, explaining what VCR mode does:
Another description provides a more technical description of the issue that Automatic Frequency Control will correct: “It will also occur when the receiver is operated from a signal which does not have horizontal slices in the vertical sync block.” Apparently, the Sega Master System doesn’t have horizontal slices in the vertical sync block, which explains the root cause of the issue. Without AFC, or a way to re-generate the horizontal frequency (such as by using a 580xi), the SMS can never sync to a BKM-68x.
Board Pictures:
Here’s a link to detailed pictures of the board itself, in case anyone’s interested in the circuitry: https://mega.nz/#!R1sFCZpQ!vxTkUyGhEe4fDaJ8nfUp5vyVETV6JhBlwVNy-KYX7g0
Manuals:
XGA was nice enough to donate both the operational manual and the service manual for the 68x:
BKM-68X maintenance menu:
XGA also provided a guide on how to access the maintenance menu of the 68x itself, which isn’t in the manuals. Also, the main A-series maintenance password is 53415.
This is how you access the BKM-68X maintenance menu and also the options that are available (I don’t believe these options are listed any either of the operation manual or service manual for either the A20F1 or the BKM-68X). If anyone has any suggestions on what options to enable / disable to get it to sync properly with consoles like the AES, please speak up.
1) Press the MENU button and select “SYSTEM CONFIGURATION…”
2) Select “MAINTENANCE…”
3) Enter the password 53415 and press enter
4) Select the “BKM-68X…” option
Page 1 options
Page 2 options
Page 3 options
Conclusion:
Unless you’re a “BVM collector”, there’s absolutely no reason to try and use, or acquire the original 68x. Martin’s homebrew replacement is better in every way and unlike the original, it’s well worth the money.
If you already own a 68x, I’d suggest trying some of the workarounds mentioned above, just to hold you off until a true sync regeneration box is released.
Here’s links to the main Service Manual Page and the main RGB Monitor page. Also, feel free to check out the main page for more retro-awesomeness.