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For those who have the OBUB-1 or OBUB-2 that pre-date the V2.0 MSS Standard:
The OBUB-1 and OBUB-2 are compatible with the V2.0 MSS Standard, which is tailored to
avoid compatibility issues with legacy MSS products developed under the predecessor
V1.0 MSS (the original Rail Model Journal article published in 2005).
However, the OBUB-1 and OBUB-2 don't support some new features of the V2.0 MSS
Standard, including "Approach Diverging" aspects associated with junctions (this feature
uses MSS Occupancy Bus pin 8, which is no longer assigned as MSS Ground) and
"alternate functions" (this feature can use pin 7, which was historically tied to MSS
Ground and is still the default use for pin 7 in the V2.0 MSS Standard).
There is no easy way to modify the OBUB-1 or OBUB-2 to support these new features.
Upgrading to the OBUB-3 is one path forward to enable use of the Approach Diverging
feature or pin 7 for functions other than MSS Ground.
Another change in the V2.0 MSS Standard is that 12VDC is specified for powering all MSS
electronics. Some OBUB-2's have a 9 VDC regulator installed. There is no harm in leaving
such OBUBs as-is; however, to update to 12 VDC simply replace the VR1 component with
Digi-Key LM2940CT-12/NOPB-ND or an equivalent device.
OBUB Instructions Archive