Hi Richard
Sandisk cards work very well, but you have to make sure they are not fakes. I always buy from Amazon (not Amazon Marketplace), or My Memory. Amazon UK are doing the 200GB car for £65.99 at present. (The 256GB is a bit expensive at £125)
Re it being locked, is it stuck on a particular screen? Will it switch on/off? The following may help:-
What to try if the FiiO players cannot be turned on or freeze?
http://fiio.me/forum.php?mod=viewthread&tid=40697&page=1&extra=#pid108982
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Regarding Key-lock settings
http://fiio.me/forum.php?mod=viewthread&tid=42608&extra=page=1
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Re your previous queries/observations, have a read of the following:-
From X7ii User Guide
Why does the X7 get a little hot in operation?
A: The X7 utilizes an SoC with high clock speed, a separate DAC, and (also separately) a high power
headphone amplifier and independent analog volume control in the amplification stage, thus
dissipating way more power than consumer DAPs typically performing computation, DAC and
amplification all on the SoC. Apart from outputting more power to your headphones, a lot of this
power is also dissipated as heat, thus causing the X7 to heat up slightly in operation; but this does
not endanger the X7 or the listener in any way.
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Why is the X7 a bit sluggish in responding at times?
A: a) High bitrate lossless tracks, particularly 384k/24bit APEs or DSD files, take more hardware
resources to decode, possibly causing slowdowns in the player UI. You may convert such APEs to
FLACs or uncompressed WAVs using programs such as foobar2000 on the computer first to make it
easier on the player. The sound quality will be the same.
b) Massive songs stored in the micro SD card might also result in operation delay.
c) Massive files of non-music formats like photos, videos stored in the Micro SD card might cost
extra time on identification.
d) Playing high bitrate files or DSD files from slow micro SD card might cause stuttering. Class 10 or
above genuine micro SD cards are recommended.
e) Disordered files (such as various APE albums and CUE files all put into one folder) might slow
down the loading speed. It's recommended to create folders in this method: first create folder of
different artists then create subfolders of different albums under the artist folder.
f) Different formats or bit rate files stored together might increase processing time. It's
recommended to create different folders to store different format files and choose playback by
folders to avoid X7 switching decoder frequently
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Regards, Dave