It sounds like it needs to be flashed/programmed with a version of the PRO-652 software. I don't believe it should say anything about the PSR500 version on the display when booting. Possibly someone tried to update the software for this scanner with a file intended for the PSR500?
I have a copy of the CPU updater for the PRO-651 which should be the same as for the PRO-652. If you would like a copy just send me your e-mail by private message.
You could also try plugging in a pair of headsets into the headphone jack to see if those work. It could be a dirty or defective headphone jack causing the problem.
the PSR 500 text is / can be programed when the scanner is programed with software , I know in arc 500 you can make that boot up text say anything you want . I have mine set to say property of and my name and callsign .