Revamp Vintage Radio: Epic Bluetooth Upgrade!

Do you own a classic HSAE RDC radio with exceptional sound quality and a rear USB port, but lacking Bluetooth capability due to its older model? Elevate your audio setup by incorporating a Bluetooth module and optimizing the auxiliary function.

In case your initial modification attempts have hit a roadblock, here are some potential solutions to consider:

Model Check: Verify your radio's specific model online to explore available guides. Certain versions can access the AUX mode via a mode button.

AUX Mode Activation: Your radio can be triggered into AUX mode by grounding the TEL pin, resulting in the display showing "TEL-IN."

However, if you're encountering difficulties inputting audio signals through AUX_GND, AUX_L, and AUX_R, your circuitry might be at play. Examining the board layout, it becomes apparent that the AUX signal routes through the radio chip. By linking the audio input of the amplifier, post radio chip, normal audio output is achieved. This suggests a potential issue with the radio chip, an NXP TEF663.

The radio chip is capable of delivering audio through DAC outputs to the amplifier, with four routes available. While the original AUX input was connected to AIN1, a deeper exploration found AIN2 and AIN3 unconnected, with respective capacitors C140-C143 absent. Experimenting with AIN2 and AIN3 proved successful. Transitioning components such as C28, C32, and C33 from AIN1 to C140, parallel connection of C142-C143, and introducing a flywire to CON1 resolved the issue, enabling external audio playback.

If considering vehicular use, it is advisable to introduce a switch connected to ACC (accessory power). This switch can replace the mute button, which will help manage power consumption (0.2A) during key transitions and engine ignition. Additionally, relocating the rear USB port to the front panel, as depicted in Figure 2, is also feasible through manual assembly.

Elevate your radio experience with these enhancements, opening doors to a versatile and improved audio setup. Embrace modern convenience while preserving the timeless charm of your HSAE RDC radio!