Hi, after replacing the fuse resistor R238, the right channel nicely started to work! and right channel speaker connectors are liking DC: 0,0V
At this point it seems half of the problem was fixed.
The output from the left side is liking now DC: -17,6V (there was a change in the polarity)
I have checked the R261 and R262 green resistors and they appeared to be in a good condition: Nominal value for them is 6,8ohm, and the measured value was 7,2ohm for both of them.
This is the new table of volts I obtained by measuring the stk0039 pins:
PIN1: 19,1 / -1,2 (VOLTS Left / VOLTS Right channel)
PIN2: 35,2 / -35,1
PIN3: -17,4 / 0
PIN4: 0 / 0
PIN5: -33,9 / -34,8
PIN6: 0 / 0
PIN7: 0 / 0
PIN8: -17,8 / 0
PIN9: 35,4 / 35,5
PIN 0: -16,2 / 1,3
As you can see the values for the right channel (actually working) turned to be close values, as written in the Solderdude schematic.
I checked the resistances R249, and R251, and they are fine (I don't understant from where are coming the -16v negative in pin 0 of STK).
I don't know where is the problem with left channel now
Thanks for your help