This stereo has 4 main IC involved in setting the 5-CH analog inputs, the main MCU, an analog switch for all the channels, and 2 for all the CH volumes.
I bought it used and in no time I was having problems either changing input source, or changing volume, maybe both.
But now today I'm back probing the MCU, and it seems the MCU is only sending the volume data, when I change input source, but not when I only turn the volume knob.
However, the same MCU still sends the updated volume dB level to the display. So I wonder what could be going wrong with the MCU ? It's a Toshiba TMP88CU74F, something similar to the TLCS-870 family and Zilog-80's before those iirc.
But there's not much info on them, does anyone know if these old Toshiba MCU's are hackable in anyway ? There's no external RAM/ROM. Are there any old Toshiba datasheets and instruction sets ??
I guess there's no hope of fixing it, but for now I can learn how to read the digital volume knobby, and I already know the format of the volume data, and was working on a program to read and send data to these IC's at a way slower speed.