Why do I have a black display with the message ''7s onkey press''?

[djolew]

Black display with message ''7s onkey press''

On the phone the Samsung Galaxy Core me from time to time appears black display and writes
7s onkey press
Please if you can explain to me what to do to prevent this from happening.
Thanks in advance

 

[B. Diddy]

Re: Black display with message ''7s onkey press''

Welcome to Android Central! Does it seem to be associated with any particular app or action? Does it only appear briefly, or does it freeze that way? Are you rooted or unrooted? Have you tried a factory reset?

 

[rebroad]

You (or someone else) probably recently enabled some sort of debugging using the various *# codes on the dialpad. You can disable these in the same way as you enabled them. The key code is probably *#9900#