I bought this Roland TR-505 as “for parts/repair” as it didn’t start at all according to the seller. After a little investigation it became clear that it did work on batteries and it was just the power connector on the main board that had issues. One of the pads the connector was soldered to had detached from the board and the trace it was connected to.
I soldered a wire between the power connector and the pad where it was supposed to go. Then it started as it should.
Otherwise the unit was very dirty and hand residue from various tape and lables on it so this was also cleaned up. The volume pot was very noisy so I cleaned this.
The battery hatch was unfortunately missing and also the back plate around the connectors, but I don’t think it is worth the effort to try to find these prise wise