Sounds buttons up works but not down.

Stephen, The 1st link is a disassembly guide which will get you inside the Tab to check the volume button from the inside to see if it is sticking/dirty, can be repaired or you may have to replace the Power/volume button flex shown in 2nd and 3rd link. Always verify part correct for your device before placing order. You can also do a search for better pricing perhaps using full model#. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.

Samsung Galaxy Tab 3 8.0 Display Assembly - Touch screen & LCD Display Replacement

http://www.ebay.ca/itm/OEM-SAMSUNG-GALAX...

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