CRT:BKM-68X

The BKM-68X is a rare optional input board used for adding RGB/YPbPr component inputs to a BVM-A series monitor. While they are rare, expensive, and often have sync related issues - there exists Martin Hejnfelt's BKM-68X clone (source files) which has all the same functionality but for a fraction of the price and with less sync issues as shown in the picture below.



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 BVMs offered, which cleared up a lot of the horizontal problems. Different settings for the card's configuration, as well as a lot of "tricks" to fix the sync. A sync regeneration device 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:
 * 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 & Sega Master System
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 an original BKM-68X. The BKM-68X clone does not have this problem.

BKM-68X Maintenance Menu
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...". [[File:BKM-68xMaintenanceMenu01.jpg]]
 * 2) Select "MAINTENANCE...". [[File:BKM-68xMaintenanceMenu02.jpg]]
 * 3) Enter the password 53415 and press Enter. [[File:BKM-68xMaintenanceMenu03.jpg]]
 * 4) Select the "BKM-68X..." option. [[File:BKM-68xMaintenanceMenu04.jpg]]

Options:



Media
BKM-68X clone developer log on ImmerHax website



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