It's the correct sound board. That's a WPC pre-DCS sound board. I know because I blew one up as well. Not once. But twice.
It's likely continuity is present due to the carbon all over the place. Carbon conducts. You need clean all the debris and check the pads and traces.
Double check the AC voltage coming in to the sound board (J501). Make sure it's somewhere around 18VAC across GRY and GRY-WHT as well as GRY-WHT and GRY-GRN. It should be 36VAC across GRY and GRY-GRN.