I'm not affiliated with this sale. Owner says was great 10 years ago when last in service... but why not grab a little speaker wire and at least confirm both channels are working? That seems odd but he's asking about half what they tend to ask lately.
https://austin.craigslist.org/ele/d/cedar-park-marantz-2285b/7304468576.html
https://austin.craigslist.org/ele/d/cedar-park-marantz-2285b/7304468576.html