This Yamaha DX7 had intermittent connection issues with the audio output; if the cable was touched the audio would either drop out or come back. After some troubleshooting I came to the conclusion that the terminals within the jack had been pushed back over the years so they didn’t make proper contact with the cable plug all of the time. The solution was to desolder the jack, open it and bend the terminals back so they would push harder on the plug.
I/O Board still in the unit 
Board removed from unit 
Jack desoldered 
Jack opened to be able to access the terminals
