Kenwood TM-2550A trouble
 

I have a trouble with my old TM-2550A.
When I turn it on, the unit does not show the display, only the red TX
light turn on without pressing any button, even PTT.
I tried to reset the CPU shorting the two pins located on the lower
board. Also, I measured the CPU battery backup, showing 3,2 V aprox.
(after 15 years?).
Then, I test the pwr and has no output (0 W).
Any ideas, and an schematic diagram would be well appreciated.
Claudio - LU3CFA