Well there is something I can do for you. If you are in warranty, send it back but if not, don't be afraid to tackle it yourself. The volume wheel seems to be the rio's main weak spot. Mine broke twice and i have been able to repair it both times.
1 tube 2-part epoxy glue
1 bottle methylated spirits
1 sewing needle
some pieces of paper or other disposable surfaces
The following link shows photographs of someone else opening their rio (hard enough to do at first) with useful instructions in the captions.
I advise opening the device with rigid plastic implements instead of screwdrivers to prevent damage to the exterior or the player and the components inside. Don't be afraid of using a bit of force in taking of the back casing. Once you have a tool inserted through the bottom of the device, (no innuendo intended here :-) ) you can lever the back cover off.
First clean the surfaces to be glued with the sponge soaked in a small amount of methylated spirits and let each dry.
I used 2-part epoxy glue available in a hardware shop. I mixed a blob of this on a piece of laminated paper and applied some of it to the two fracture points on the wheel with the eye of a large sewing needle.
I did a few practice runs with pieces of paper before i went for the real thing. You have to be careful because the two points to be re-attached on the player are very small and are very close to moving parts.
Once the glue is on and you are happy with its neatness, place the wheel back on the player as best you can so that the fractured points match up once again. marking the back of the wheel may make this easier. Then hold the wheel and player tightly together with your hand with your thumb on the wheel for 15 minutes. You can rotate the wheel to ensure that the glue has not adhered to moving parts. Be patient and keep the bond still. You may have to reapply the glue if after the 15 minutes if the two surfaces have not been adequately bonded. Remove the glue from both wheel and player with Methylated spirits and the sponge and start again.
Once the glue has been let harden for 15 mins and you are happy with it (test it gently by slowly rotating the wheel while the carbon is on if you like), leave the rio in a safe place for 24 hours after which you can re-attach the back cover and once again enjoy your music!!
This is a problem with alot of small electronics these days. If and only if you feel comfort with taking this unit apart will it help correct the problem your having.. My recomindation would be to send back to the manufacturer because Im sure this is not the first case history they are having with this model as there are really no serviceable parts for the consumer as well a good service tech. These are all surface mounted switches and buttons that do break off at the cabinet level. Not alot you can do sorry man.
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