Samsung DeX usually works without much fuss, but a few factors can stop the connection to a monitor, TV or computer from happening properly. In many cases, the problem comes down to the cable being used, the device's settings, or the way the connection was made.
Since this information tends to be scattered across support pages and user reports, pinpointing the cause isn't always easy. So I've gathered the most common situations here, with their likely causes and the guidance available for each one.
No image, or a cropped image, using the DeX cable or USB-C to HDMI
One of the most common problems happens when the phone is connected to the TV or monitor over an HDMI cable and the external screen shows no image at all, or shows it with the edges cut off. In many cases this comes down to an incomplete cable connection, or to the TV/monitor's picture format setting.
- Check the cable seating: unplug the cable from the phone and from the TV or monitor, then plug it back in, making sure the connectors are fully seated. If the phone has a case on, it's worth removing it temporarily for the test — it can keep the cable from seating properly.
- Confirm the cable actually carries video: not every USB-C cable can send an image — some are charging-only. See how to choose the right cable or adapter before hunting further for a fault.
- Adjust the picture format on the TV or monitor: if the DeX interface shows up cropped at the sides, open the TV/monitor's picture menu and look for the screen size (or aspect) setting. Select "Fit to screen" or "16:9" until the image displays correctly.
USB-C hub or dock without external power
When using a USB-C hub or a dock like the DeX Station, the monitor may show no image and DeX may not start even with every cable connected correctly. One possible cause is the accessory not getting enough power: some hubs and docks need to be plugged into an external power source to work with DeX.
- Check that the USB-C hub or dock is connected to a compatible charger with enough wattage. According to Samsung's support guidance, standard-speed chargers may not deliver the power DeX needs on these accessories.
Worth noting: in the Samsung community, one user reported that the failure persisted even after following this guidance. In that case, the problem may be related to other factors in the device or the accessory being used.
Lag, freezing or no signal on wireless DeX
When trying to use DeX without a cable, you may run into response lag, freezing or even no signal on the external screen. These situations are usually related to device compatibility or to the stability of the Wi-Fi connection.
- Check the Wi-Fi connection and how close the devices are: make sure the phone or tablet and the external screen are on the same Wi-Fi network, and keep the devices close to avoid instability.
- Check device compatibility: wireless DeX has some limitations. It doesn't work with touch screens, with the Galaxy Z Flip line, or with the Galaxy Tab S4.
- Adjust zoom and font size: if the connection works but everything looks out of proportion on the screen, go to Settings > Samsung DeX on the mobile device and adjust the zoom and font size options.
- Enable the right mode on compatible tablets: on some tablet models you need to go to Settings > Connected devices > Samsung DeX and enable "Classic" mode to allow casting to an external screen.
The external screen only mirrors the device instead of starting DeX
When connecting a Galaxy phone or tablet to an external screen, the monitor or TV may show the exact same image as the device instead of opening the DeX interface. This can be related to changes after software updates, to the selected display setting, or to the connection between the device and the screen.
- Check for device updates: after updating to One UI 8 (Android 16), some Galaxy phones and tablets may start in mirroring mode instead of opening DeX. Check for updates under Settings > Software update.
- Check the cable and the connection: make sure the device and the external screen are connected through a compatible USB-C to HDMI cable or adapter.
- Start DeX manually: swipe down from the top of the screen with two fingers to open quick settings, then tap the DeX icon.
- Change the display setting: if the external screen keeps mirroring, go to Settings > Connected devices > Samsung DeX, select Connected screen and switch the option to Extend.
- Try another screen: if the problem persists, connect the device to a different monitor or TV to check whether the failure is tied to that screen's compatibility. Another option is trying wireless DeX, where available.
Power saving mode turned on
Some users have reported trouble using DeX together with power saving mode. The reports describe situations where the feature isn't available while DeX is running, or problems that appeared after trying to enable power saving through other paths.
According to those reports, while DeX is active the option to enable power saving mode may appear greyed out in the notification panel. There were also cases where users enabled the feature and then struggled to start DeX again — even after turning it off and restarting the device.
I couldn't find an official solution for this one — the reports come from Reddit users and are a few years old. So this section is here only to give the problem some context, based on the situations described.
Wireless DeX and VPN conflicts
Some users have also reported trouble using wireless DeX while a VPN was active on the device. In those cases, DeX may fail to find the external screen or to connect to it.
Based on the reports, the problem seemed to happen in the communication between the Galaxy and the external screen while the VPN was running. Some users mentioned trying to change VPN settings or whitelist certain apps, without a definitive fix. Others ended up disabling the VPN to use DeX, or falling back to alternatives like mobile data.
No official solution here either — only scattered workarounds that may help in specific setups, like split tunneling. That's why I'd rather give the problem context based on the reports than suggest a path I couldn't confirm.
There isn't always a single cause
It's not always easy to pin down why a DeX connection fails, since different factors can interfere with the feature. In many cases, a few small checks are enough to find the cause — or even fix it.
The goal of this note was to gather this information in one place, to make the most common problems easier to identify and to lay out the guidance available for each case. Where no official guidance exists, the goal was simply to give the problem context based on what turned up during the research. This note is part of the Samsung DeX complete guide.