I’ve acquired a used Mk1 Shelves in a module swap. It sounds killer but the low-mid filter doesn’t do anything. All the chips have power and CVs are passing into the circuit. However, my attempts to troubleshoot any further are possibly thwarted by my lack of understanding of how the 2164 VCAs work, particularly because they’re connected directly to the OPA inputs inside the filters as well as to the plus/minus busses. Taking measurements on a current-based circuitry (without breaking it) isn’t something I’ve done.
A saner person would just send this to Emile, but I’m an intrepid hardware hacker on a quest. Any light that could be shed on the theory of operation of the filter* as well as troubleshooting steps to narrow down the culprit would be greatly appreciated.
*PS …including what makes that filter “Low-Mid” when components seem identical to the “Hi-Mid”? I may be “missing the forest for the trees” here, to use the saying.