Since both channels are not working, I can think of several possibilities:

1. Protection circuit problem
2. Blown fuse
3. Burnt out transformer

If you do not have basic electronic skills, it would be best to refer the troubleshooting and repair to a qualified service technician. Fixing such equipment require the right tools like an oscilloscope, audio signal generator and multimeter. If you would like to pursue this further, you can download the service manual from this site. It will cost you though.

http://www.servicemanuals.net/Servic...1/results.aspx