Description

Symptoms

In some setups, the Bluetooth module may fail to start correctly when the device is powered on. This can result in:

• Bluetooth not appearing or being discoverable after startup
• Failure to establish a Bluetooth connection
• Bluetooth functionality returning only after the device is power-cycled

Cause

This issue has been observed with certain power supplies that gradually ramp the output voltage when power is applied from the mains.

When the power supply is switched on, the 9V output does not immediately reach its nominal voltage. Instead, the voltage rises slowly over a short period of time. During this ramp-up phase, the Bluetooth module may receive a voltage level that is sufficient to begin startup but not stable enough for proper initialization.

As a result, the Bluetooth module may enter an invalid startup state and fail to initialize correctly.

Affected Configurations

This behavior has been observed with some Strymon power supplies when the power supply itself is switched on from the AC mains.

The issue is generally not related to normal operation once the system is fully powered.

Workarounds

If you experience this issue:

1. Ensure the power supply is already powered and stable before connecting power to the device.
2. If Bluetooth fails to start, disconnect and reconnect power to the device after the power supply has fully stabilized.
3. Use a power source that provides a faster rise time during startup.

Additional Information

The issue is caused by the startup characteristics of the power supply and not by Bluetooth communication itself. Once the device has powered up successfully, Bluetooth operation is unaffected.

Hardware Fix

There is a hardware fix that involves soldering a 10uF - 47uF electrolytic capacitor to the board. We recommend just using a 47uF capacitor for more margin. If you have access to a soldering iron and the component, or to an electronics repair shop, this fix can easily be done.

1. Remove the MC8 PRO backplate
2. Look for the capacitor C9 near the bluetooth module. This is where we will solder the capacitor

3. Take your electrolytic capacitor, trim the leads and bend the leads to this position.

4. Solder the capacitor here and make sure the pins polarity are correct

For the MC4 PRO, the capacitor is located towards the bottom of the board:

5. This will delay the boot up of the bluetooth module to just after the power supply is stable. We have tested with a 10uF and a 47uF capacitor. A larger value (47uf) will increase the delay.

Updated on: 18/06/2026