Not sure about the CDR2005 but have had a similar problem with a CCR 2006 the volume knob works a rotary (digital) encoder when you turn it ( as someone said its like tapping a volume up or down button as you turn it. ) If you pull the volume knob out and turn it, it adjusts the balance ( left/right ) and this was playing up, if you just touched the knob you lost almost all of the left or right channel... It turned out to be just be a couple of dry joints where the pots ( for balance) were soldered in ( just needed resoldering no components necessary)
Procedure was roughly:-
remove the unit, ( Make sure you have the radio code, small alan key for security screws + double din removal tool )
Remember electronics, are best done at a static safe electronics workstation by someone that knows what they are doing for both your safety and depending how paranoid you are to not damaging your radio... so don't continue if you don't know what you are doing and understand the risks ( electric shock from capacitors in the radio etc.... )
Oops, started to sound a bit like a lawyer there (which I'm not) , but basically don't blame me if ANYTHING goes wrong....
remove small torx screws on the sides which hold the plastic front panel in place
I think there where also small plastic catches which need to be moved slightly positioned sort of beween the two halfs of the unit ( radio-cass/cd-changer)
Ease the front panel off, which was plugged into the rest of the unit - watch out yours may be different and have delicate ribbon cables or something ...
Look at the volume/balance control, you can see the two pots and rotary encoder on a tiny circuit board on the back of it.
Examine the soldering on the joints for the encoder and pots.
Resolder any dry joints ( or get someone else to if you've not got the skill to do it your self.... )
Carefully inspect to check no solder had gone astray and shorting anything out!!
Reverse instructions to refit, ( though obviously dont desolder the joints
)
Not sure where you'd get replacement pots if you need them, you could try
www.cpc.co.uk, or farnell, maplin etc, maybe even try asking at your local tv repair shop....