A Samsung CU8000 that restarts by itself, turns on and off or shows the Samsung logo in a loop is usually dealing with a software update, a connected device, a power supply fault or heat, and the steps are a short list. Start with a power reset: unplug the TV for a minute, hold the power button on the TV for fifteen seconds to drain charge, and plug it directly into a wall outlet and not a power strip. Remove all connected devices, including HDMI sources and USB drives, and see whether the TV runs alone, since a faulty device or a corrupt USB drive can cause a boot loop. Add devices back one at a time to find the culprit.
The checks in more detail
A device connected through HDMI-CEC can also switch the TV on and off, so turn CEC off in the TV's settings as a test. Check the software. In Settings, Support, Software Update, update the TV, and turn on Auto Update. A restart loop that began after an update may be cured by a reset: Settings, Support, Self Diagnosis, Reset restores the defaults, though you will lose settings and have to sign in again. If you cannot reach the menu, hold the Return and Play/Pause buttons on the remote for several seconds as Samsung describes for a reset, or use the TV's own button.
Watch for patterns. A TV that restarts after some time of use may be overheating: check the vents at the back, give it space and clean the dust.
A TV that restarts when the picture gets bright points to a power supply that is struggling, a known cause in older sets, so try another outlet and lower the brightness. A TV that restarts when a specific app is opened may have a bad app; remove and reinstall it. Check Eco settings such as Sleep Timer and Auto Power Off, which turn the TV off by design. If the TV clicks and will not power on, or the standby light flashes in a pattern, note the pattern for service.
If it persists, contact Samsung with the model and serial number. With a CU8000 that switches itself off or restarts, note the pattern before anything else. A set that restarts only when a particular app opens points at that app, so update or reinstall it;
a set that restarts at random times with nothing running points at power or heat. Look at the power cord and the outlet: a loose plug, a worn extension lead or a surge strip that is failing shows up as random restarts, so connect the TV straight to a wall outlet for a few days. Samsung's Eco Solution settings include an automatic power off after a period without input, and Sleep Timer, which can be mistaken for a fault. Check the vents on the back for dust, and leave a few centimetres of space round the set, since an edge-lit panel inside a tight cabinet runs warm. Unplug the TV for a full minute and hold the power button while it is unplugged to drain the board.
Differential
Likely causes of “Samsung CU8000 Crystal UHD TV keeps restarting or will not stay on”, and how to tell them apart
- 1
A stuck power state
What separates it The TV will not finish starting
How to confirm Unplug and hold power for fifteen seconds
- 2
A faulty device or USB drive
What separates it A boot loop with devices attached
How to confirm Remove them and add back one by one
- 3
HDMI-CEC switching the TV
What separates it It turns on and off by itself
How to confirm Turn CEC off as a test
- 4
A struggling power supply or heat
What separates it Restarts under brightness or after use
How to confirm Try another outlet, clear the vents
- 5
A bad update or app
What separates it Restarts after an update or an app launch
How to confirm Update, reset or reinstall the app
Before you touch a setting
Record this first — changing settings destroys the evidence
- When the restart occurs
- Devices connected
- The standby light pattern
- The software version
Try in this order
0 of 6 completedUnplug and hold power
ReversibleFor fifteen seconds.
Plug into a wall outlet
ReversibleNot a strip.
Remove all devices
ReversibleThen add them back.
Turn off CEC
ReversibleAs a test.
Update or reset the TV
ReversibleIn Support.
Contact Samsung
ReversibleIf it persists.
Model-specific
What is true of this model and not of its siblings
- CEC
- Connected devices can switch the TV.
- Power
- A wall outlet is better than a strip.
Stop boundary
When this stops being a self-service repair
- !If it persists after a reset, contact Samsung with the model and serial number
- !Note the standby light flashes
- !Do not open the TV
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why does my CU8000 restart?+
A software state, a device or power.
Can a USB drive cause a loop?+
Yes.
Can CEC turn it on and off?+
Yes, from a connected device.
Will a reset erase my settings?+
Yes.