Thanks you very much for this "hard to find" service manual.
Will help a lot in repairing this tuner.
Text excerpt from page 4 (click to view)
CPU (LSI101: MSM6387-22)
Containing a sound data ROM and a DAC (Digital to Analog Convertor), the CPU provides sound waveform in accodance with the pressed key and the selected tone. The following table shows the pin functions of LSI101.
Pin No. 1, 2 3 4 5 6 7 8 9 10 11 ~ 18 19, 20 21 ~ 30 Terminal TEST1, TEST2 RESET AVDD OUT AGND GND COSI COSO VDD KI0 ~ KI7 KO11, KO10 KO9 ~ KO0 Out In In Out In In In â In In In/ Out Function Not used. Connected to ground. Power ON reset terminal. On: +5 V +5 V sorce for the built-in DAC Sound waveform output Ground (0 V) source for the built-in DAC Ground (0 V) source 21.725 MHz clock pulse input Not used +5 V source Input terminals from keys and switches Not used. Key and switch scan signal outputs Off: 0 V
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the waveform.
AVDD Q101 2SC1740SQ R2106 C106 C108
To power amp
Amplifier/Voltage Regulator (IC101: AN8053N)
The right figure shows the internal block of IC101.