I recently purchased a faulty Roomba 676 and wanted to try to fix it. The problem was it not charging. I tried to charge it on a 676 station and it worked fine, so I assume no issues with the Roomba itself.

I tried measuring the voltage from the station pins and it was fluctuation between 0 and 10 V, which the good station does not do.

I open the station up and find 2 different PCBs, one working as the PSU and the other with the intelligence. The boards are connected with wires. I cut the wires and try to measure the voltage coming from the PSU board and it is also fluctuating between 0 and ~23 V. When I connect a seperate PSU directly to the "intelligent" PSB, I get a steady 2V out and when I connect the pins with a 10K resistor, the voltage ramps up to about 20 V, so I would say that PCB is working as it should. The problem is somewhere in the PSU PCB.

Measurement after PSU PCB

Measurement of the charging pins