Defect

The first thing you can try is to check the wiring connections between the stereo and the speakers. Make sure that all of the connections are secure and that there are no loose wires. If the wiring connections are all good, then you may need to replace the preamp or have the Auto-turn and off function repaired.

Here are some additional troubleshooting tips:

Try disconnecting the stereo from the battery for a few minutes and then reconnecting it. This can sometimes reset the stereo and fix minor problems.

Check the stereo's firmware for updates. If there is an update available, install it. Outdated firmware can sometimes cause problems with the stereo's features.

Try using a different power source. If the stereo powers off correctly when you use a different power source, then the problem is likely with the stereo's wiring or power supply.

If you have tried all of the above and the stereo is still not powering off correctly, then you will need to take the stereo to a qualified technician to have it repaired.

Please note that I am not a qualified technician and I cannot provide specific repair instructions. If you are not comfortable troubleshooting the problem yourself, please take the stereo to a qualified technician to have it repaired.