Few moths ago, my mother come back from Italy and brought me a digital radio in the form of an car (Porsche Cayenne ?)
it is cool, no ?
The problem, on every boot, the volume is set to 84% ... It's very noisy !!
I don't understand why each FM frequence are saved into the memory but is not the case for the volume ?
It is why i decide to try to control the volume from an external potentiometer
Step 1: Identifying the Amplifier Chip
After i have identified the amplifier chip : an MC4863 (Dual 2.2W Audio Amplifier) i download the datasheet to understan how the gain it is controled
I found the following text and image in the datasheet:
The first amplifier’s gain is externally configurable, while the second amplifier is internally fixed in a unity-gain
The datasheet talk about a resistor of 20Khom to control the external gain but on the PCB i have found only two resistors of 67Khom ... may be to have a gain > 1 ?
Step 2: Build a Dual Potentiometer From Two Traditional Potentiometer
The Chip MC4863 is a dual Audio Amplifier so that means it has two independent output signals ... which mean it require two different potentiometer in one package
I don't have one, so i build it one ...
Step 3: Fix the Dual Potentiometer
After the dual potentiometer is done, i fixed it on the car (I couldn't fix it where i wanted to fix it initially)
Step 4: Replace the 67Khom Resistors by the DIY Dual Potentiometer
It is very delicate to disolder SMD components because the PCB copper layer can unstuck
It is why i do this step at last