I had much problems with my Kenwood TS140-S and no Circuit Diagram..
The digits of the display began flickering after about 10 minutes and the display showed nonsens. The relais of the PA made much noise... After switching the trx off it worked again .. for ten minutes.
The kenwood homepages were no help either...
I opend it carefully, disconnected all HF connectors and cleanded them with a rubber gum ( I donīt know the exact term, but I mean that thing I drove my teacher mad in drawing ! ) and it was a little better. After a tip from packet radio, I removed the EProm on the Upper platine (circuit board) and cleaned its legs V E R R Y carefully on the same way. Now the TS140S works propperly since 8 weeks.