I got a second hand PO-35 Speak and one of the buttons did not work. Everything else worked normally but one button didn’t trigger.
I found this guide and followed it to clean the push buttons on the pocket operator. It worked like a charm! I hope this helps anyone with a similar issue.
https://www.ifixit.com/Guide/How+to+Fix+the+Buttons+of+a+Pocket+Operator/141451