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Don, The audio amplifier for the headphone jack is IC404. You should check it for proper bias voltages. I didn't see if you wired the radio for 9v or 12v, but you should find a little less than half that voltage on pins 1,2,3,5,6&7 of IC404. That voltage is supplied by a resistive voltage divider made up of R423 and R424. If those voltages are good, then you will need to inject an audio signal into the inputs (it's a stereo amp connection) pins 2 and 6 and look for them to come out on the left and right channels. If that test is good, then you may have an issue with the D/A converter IC401or the RC filter circuit between it and IC 404. Refer to the schematic and parts layout diagram for the above parts. Good luck ... Ron