One of the D1200719 current driver boards (S1500270) was in the EE shop for repair after some unexplained current fluctuations were seen.
Previously I measured its output at different knob settings, and saw saturation when driving a 25 Ω load. The saturation happens when the low frequency current source block reaches its voltage limit. (This wasn’t seen in Zach’s previous test, probably because a lower-impedance load was used.)
The board has now been upgraded from v4 to v7, to fix high frequency oscillations and crossover issues. An annotated schematic is uploaded to the board’s DCC traveler.
A few tests were made to check the basic functionality: