Thanks for your help.
I found the Kenwood technical notice this morning. And it contains the
electrical diagram and more...
But i haven't the link on my personal computer: I will to post it next
week on the news group.. when i will come back to my work
I found also why the TH78 wouldn't start: It miss a 5V (called "5M" on
the diagram) on a CPU-card. Probably because a cut wire into the card...
Now, my TH78 is started again... but the VHF squelch failure remains..
Fred