Sir Rick79 . . . . .
All its mass inter page complexity, is now simplified down to a one page
UNITIZED draw out .
Initially take note of the left IC1601 System Control and its pins 38----41 as being its Analog to Digital conversion inputs and each is receiving a voltage reference from the R1627---30 from a common B+ supply buss and a bit of capacitive decoupling to ground..
Then you follow the
YELLOW BRICK ROAD path to the right, where it then travels to the keyboard and break out again as
AD1-AD2-AD3 and AD4 and serving 4 cluster strings of keyboard switches.
Refer to your
AD1 line which relates to your
TREBLE + function and you see that pressing that button will cause a voltage shift at the u/p, and that voltage is detected and converted to a digital value of serial 1 & 0's and that then feeds to the dedicated chips that do your digital tuning audio switching and audio control functions.
You can see that the MUTING button shorts that voltage reference voltage resistor to ground for 0V.
The next INPUT MODE button shorts a 470 ohm resistor to ground to make a 10K /470 ohm voltage divider for that produced reference voltage into the AD1 converter internally.
Your TREBLE + then shorts a series 470 and 1K ohm resistor pair to ground.
Then each switch, to the right, progressively going on down the, line causes less of a voltage shift for its produced voltage reference for their distinct functions.
The 22K and 47 K's down on the end have lesser effect on the voltage reference . . .
HOWEVER . . . they have all been selected values to produce distinct voltage stair steps.
You need to be concerned on checking the circuitry associated with the AD1 buss, and the first three switches and R112 and R111 associated with them would be most suspect.
That's potentially only 10 interrelated functions.
I could not relate a pushbutton function, as being a snooze function . . .fill me in on its labeling.
RELEVANT UNITIZED SCHEMATIC SNIPPET . . . .
73's de Edd
.....