Audio 10 radio/Cassette + 6 disc CD

[paddler]

My stereo only has front speakers none fitted to the rear parcel shelf and the one in the drivers door has died (very low volume).
I'm not sure what to do Thought of going to a stereo specialist and having front speakers replaced and rear's fitted but not sure if it is the front door speaker or the amplifier which has died.
other option is to replace the stereo but don't want a non MB unit any suggestions on best route to try?

 

[armitphi]

expose both speakers (Take door panels off ) remove both speakers noting which is which .... then swop them over .. if fault migrates ... then its the speaker if not ... its the head unit