Unfortunately, Amazon shipped me the wrong breakout board from Adafruit. Not an uncommon occurrence these days. That said, I will likely spend some time to probe and record signals on each of the connectors coming into PB121. Just to make sure I understand them all and what their ranges are. For example, I need to ensure that all voltages are under about 5.5-6.0 V to avoid damaging anything. Some of the signals to/from PB121 are 8 V as is common in VCO circuits. And then verify that certain signals are control voltages versus digital logic.

I will be first wiring up the front panel connections. Everything that isn't the PLL.