Elnaldo, those were insightful comments, and although I never got to checking the components you suggested since the problem was more obvious than that, they did help me think about the problem. To answer your question, the JV+ and JV- are just test points to check the rail voltage. The JP and JM on the schematic, though, are relevant to the last problem I'm having now and with continued issues throughout this project. These are where the gates of the second set of N and P mosfets are connected to the amp when in monoblock configuration, with jumpers over to the second spot on the heat sink where the other channel's board would normally be mounted. As you probably know, there needs to be a 1k resistor in front of each gate to keep the output Mosfets stable, so that's why they're not just paralleled like the sources and drains are. In one of the photos you can see these five jumpers coming off the back side of the board and on the other the brackets on the side of the heatsink without the board. They were using what they had to work with in terms of the existing heat sink, but it's clearly a makeshift and awkward arrangement with unnecessary lengths of wire connecting output devices, some silly bare wire stock to connect the source pins of each Mosfet mounting bracket and provide a bit of structure, and multiple places where the arrangement could flex and connections could fail. To add to these problems I rewired the entire signal path with some super stiff Kimber TCX cable to improve the sound, but this made stuffing the whole thing in and out of the heatsink multiple times nerve wracking, and I had to fix broken connections a few times. Disregard the strange wire colors that don't match the circuit, I had to deal with the colors they had available and use tape to make the wires distinct. Anyway, the only remaining problem is with the amp in the pictures, and the it occurs only when I add the second pair or output devices and screw them in. What happens is it pulls one of the red wires taut and flexes the board toward the unoccupied side, creating a shorted solder joint somewhere in the two Mosfet brackets that attach to the board. When I remove the second set and nudge the board right, it goes back to normal with the ability to adjust bias and offset. The intermittency of the problem made in infuriating to diagnose. The problem on the second amp was a bad solder trace going to the upper leg of bias pot P2 that looked OK to the eye but lacked continuity. After I soldered in a clipped off leg of a resistor to that section it worked. During the adjustment process, though, I discovered that the bias is set lowest when the trim pot is fully clockwise, which is the opposite of the usual arrangement. Including this for anybody reading this thread in the future that wants to replace the low quality one turn unsealed pots the amp comes with with precision multi-turn pots: turn the bias trim pot fully clockwise before starting the bias adjustment procedure on the B&K ST-140, not the other way around! At any rate, once the trim pot was actually adjusting this amp was fine, and the other will be fine once I reflow all the solder joints on the connections between the board and the Mosfet mounting brackets. Thanks again for your help on this, Elnaldo and thanks as well to all of you that responded. Looking forward to stopping work on these and just listening to them! The two boards sounded good in the same box with the component changes I made, but I'm hoping the extra pair of output devices and added, dedicated power will create some audio magic.