The JU6400 is the entry point of Samsung's 4k TVs. It doesn't look cheap, has very little blur on movement, and delivers excellent performance for video games. Unfortunately, the picture quality in a dim room is bad (blacks will appear gray), and judder is present on 24p movies.
The Samsung JU6400 is thin, and the overall look of the TV is good. The slim borders and the stand are made of plastic with a brushed steel appearance. The fixed stand is sturdy, and has a small footprint, but is prone to collecting dust.
This isn't a good TV for watching movies in a dim room. The contrast is very low and the blacks will appear gray. The TV also has judder on 24p sources (like Blu-ray) and doesn't have any fancy features like 3D, local dimming, or HDR.
Contrast is really poor on the 55" UN55JU6400, and blacks will often appear gray. Those flaws won't be too apparent in a well-lit room. Other sizes of the JU6400 doesn't have this problem.
Uniformity isn't great, with horizontal and vertical banding that can be seen. The corners are also a lot darker. Those problems could be apparent on playing fields of uniform color.
Like other IPS TVs, the 55" one has a wide viewing angle. Colors remain saturated at an angle, though the picture darkens a bit. Other sizes of the series have worse viewing angle.
Update 01/06/2017: We have changed the methodology of testing. Since this is an old TV which we don't have anymore, we extrapolated the results from 2016 TVs.
There is a lot of cloudiness on black screens, and bright flashlighting is present on the right side.
The semi-gloss finish doesn't reflect a lot of light, and there is no rainbow around bright objects.
The TV can get bright enough for most environments.
The motion on the JU6400 is excellent. Objects will stay defined even when moving at full speed, and details won't be lost in the action. Because of the somewhat average gray uniformity, some dark patches can be seen on long camera pans over the fields.
This is the Samsung TV with the least amount of blur we've seen this year. There is a little bit of overshoot (see the trail to the left of our moving logo), but movement is pretty clear overall.
Judder in movies isn't too noticeable, but this TV cannot eliminate it without the use of the soap opera effect ('Auto Motion Plus').
Combined with its excellent motion handling, the JU6400 is great for video games. Action on the screen is well-defined, and the controls are very responsive. You can still find better options for a dedicated gaming TV, but the JU6400 is near the top.
The very low input lag is among the best you can find when you set the TV to game mode. In PC mode, the input lag is still good, at 34.9 ms.
Unlike other 4k Samsung TVs, the JU6400 doesn't do 4k @ 60Hz @ 4:4:4 (there is no 'UHD Color' option). To get Chroma 4:4:4 in the other modes, label the input as 'PC'.
The sound isn't very accurate, and doesn't have great bass. Still, it can get fairly loud, and there isn't too much distortion.
Note: Sound Quality test for TVs reviewed before 2017 was performed at 75dB, 85dB, and Max SPL. Starting 2017, the target SPL levels have been changed to 70dB, 80dB, and Max dB SPL.
Poor frequency response especially at higher volumes where pumping and compression may be present. The TV does get relatively loud, but the extension is poor.
Very good distortion results. There is a noticeable increase under maximum load, but remains with-in the limits.
There isn't a huge variety of apps, but the Tizen OS feels intuitive. The basic remote makes navigating the smart features less pleasant, but it is useful enough for navigating all the TV settings.
The 55" Samsung UN55JU6400 that we reviewed has a PLS panel (version FD05), which is a sub-category of the IPS family, and which produces grayish blacks, and has a wide viewing angle. If someone comes across a different type of panel used, let us know and we will update our review. Thank you in advance.
Some of our visitors reported that the 40", 43" and 48" version of the JU6400 has VA panels with better contrast ratios and worse viewing angles.