Hello all,
I was servicing an AX170 for a friend, and noticed the audio from the cartridge slots was very unsatisfactory. There's virtually no output of cartridge sound at all. I couldn't find service manuals or schematics, so decided to quickly reverse engineer the audio circuit.
This is what I came up with:
high res
As you can see, audio from both cartridge slots is fed almost directly to the audio outputs of the MSX. That can't be! The slot audio has to be amplified to normal line level first..
So I made this modification to the original circuit:
This mixes the cartridge audio with the PPI and PSG sound in the same way as the original design does. The signal is amplified properly now and the balance slot / PSG is about 50/50 with the 1.5k ohm value. Less gives more slot sound.
How to:
- Remove jumper J213
- Solder one leg of a resistor of 1.5k ohm to the connection of J213 closest to the resistor array
- Solder a wire beteen the other leg of the resistor and the right leg of resistor R104
Interesting fact: the T7937 MSX Engine has separate outputs for all three PSG channels. In theory it should be possible to design some kind of pseudo-stereo circuit :)
