Audio Circuit (Atari Lynx II)
The audio is pretty simple on the Lynx.
The Hayato is responsible for generating the audio.
The main audio is generated inside the Hayato after reading in the games ROM and processing the code to generate the audio output.
The audio comes out of the Right High (pin 10), Right Low (pin 11), Left High (pin 17) and Left Low (pin 24).
The High pins are treble audio, and the Low pins are subwoofer audio. If you listen to them the low sound distorted and clip a little, which the high sound pretty much like the final audio.
These can all be monitored with a speaker/amp with aux input and tapping the input to the speaker left or right channel, to check if each pin is outputting audio.
The audio then goes through the resistor array RP8 and into the 74HC04 Inverter U7.
They go out of U7 to the resistors on the right R12, R13, R40 and R41.
You can continue to probe each step of the audio path with the speaker aux setup to confirm audio is making it to each stage.
All these components are at the top right of the board.
The audio on models with Hayato chips (that don't say VLSI on) continues by going:
- R12/13 > +C16- > R42 > Vol Wheel Pin 4 > Vol Wheel Pin 3 > R93 > U5 Pin 3
- R40/41 > +C58- > R14 > Vol Wheel Pin 5 > Vol Wheel Pin 2 > R94 > U12 Pin 3
Pin 3 of each amp is the input+. Then the output is on pin 5.
So long as the amp has Input - (pin 2) and Ground (pin 4) grounded, the Vs (pin 6) to 5V and the input audio, you should get the output audio.
The gain inputs pin 8 is usually 0.7V, pin 1 gain is 1.3V (although they can be grounded and still have audio output).
The Bypass (pin 7) usually sits around 2.5V and has a capacitor to ground as a buffer.
The output audio then goes:
- U5 pin 5 > +C21- > L12 bottom > Headphone right pin
- U12 pin 5 > +C64- > L20 bottom > Headphone left pin
The inner left and right pins are shorted together. So when headphones are removed it means the outer left and right audio pins are also shorted together mixing them into mono audio for the speaker.
The headphone outer left and right pins are the left and right audio to the headphones.
When there is no headphone inserted, the inner two pins should be joined to the outer two pins. These inner pins go to the speaker left pin, with the right pin being ground.
TODO
The cartridge can send raw additional audio in on the cartridge connector pin 32, which connects to the Hayato pin 24.
This can be monitored with a speaker/amp with aux input and tapping the input to the speaker left or right channel.
Most games don't send any additional audio, and it is generated by the Hayato from the games digital data.
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