Hi Kees,
I am sorry that you are having problems with the radio. I have never heard of this happening.
J3 on the AF-Board is the connector that is used to send the audio to the front panel and swr meter. Pin 1 specifically is connected to the front "phones" jack.
If it is burned the only thing I can think of is:
1. Something was plugged into the phones jack that had a lot of current.
2. C41 (the large 220Mf cap that is connected to the output of the LM386 audio IC shorted (but even that should not cause a burned wire)
There are no power connections even close to that area.
In any case, if the wire is burned, then most likely it affected the audio amp area for the phones.
As far as skipping around in frequencies, there is only one way that I know to do this. see page 6 of the manual. the MEM button is used to skip large sections as stored memory locations. If this is not working most likely the battery needs to be replaced CR2016. In order to do that properly the top board has to be removed carefully and new battery placed on the AF board (the board you will be looking at for your burned wire issue).
I have attached some images to help.
I hope this is helpful
Guy (N1GMM)
