The objective of this modification is to provide a quality ACB stereo sound at +128 and integrate its output into the original RGB/PERITEL connector avoiding any modification on the original case. The solution is based on replacing the original sound circuit with a new one that will substantially improve the original sound quality of the equipment.In this article we will discuss the Spanish version developed by Investronica (board rev. 2 & 2-1). The English version can also be modified with the same circuit but the modifications in the motherboard as well as in the RGB/PERITEL connector are different.
Remove the computer motherboard to start. First we must cut some tracks:
|IC32 track cuts
Pins 1,4 and 5 on IC32 correspond to the three sound channels that the AY-3-8912 can generate simultaneously. With this we will be able to break the union of the outputs of the three channels that turned the sound into mono. It will be here where we will connect the new sound circuit.
circuit (component side)
circuit (solder side)
|Circuit ubication inside +128|
Now we must connect the sound input of our assembly to the sound output
of the AY. We need 3 integrated signals and ground.
We will connect pins 1,4 and 5 to the corresponding inputs of our assembly. The best solution is to solder directly over the chip pins on the components side. We will use pin 6 of the integrated as ground for our circuit. These are the only soldering we will have to do with a little more care.
At this time any sound generated by the AY will enter into our circuit directly. To add the BEEP signal we will connect the input marked as BEEP in the connection diagram with the output of the resistor R115 previously removed.
|R115 resistor connection
||GND and Left output connection|
Here we can see the original pinout of the connector and the result once the modifications have been made.
|RGB/PERITEL Original||RGB/PERITEL Modiffied|
Final aspect of the board with the new audio circuitry installed.
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