Cleaning cd lens ?

Is it wise to open the unit and clean the lens? I have a Marantz DV9500 that will not play all cds. I suspect lens is dirty. Besides a q tip what should I use for liquid ?
I use alcohol but make sure you dry it off. You need little to no pressure.
Suggest you use pure acetone instead of rubbing or isopropyl alcohol because of this definition:

"Isopropyl Rubbing Alcohol, USP / B.P. contains 68-99% of isopropanol (isopropyl alcohol) by volume, the remainder consisting of water, with or without color additives, suitable stabilizers, and perfume oils."

You don't want "perfume and oils" so stick with pure acetone. You can find this very inexpensively at your local drugstore in the nail polish remover section.
I would not apply any liquid but use a can of compressed air and blow across not directly perpendicular. There is a very thin film that usually is a filter and protectant that you do not want to possibly deform or dent.
Acetone attacks some plastics such as plexiglas. I'd be careful with that, as the lens is plastic. I use a lite swab of windex.
Thanks for the tip but I just read the ingredients on my bottle of 70% isopropyl alcohol and it states 70% isopropyl alcohol and 30% water - nothing else. I do get the sale stuff so I would have to assume that more expensive alcohol may contain stabilizers, perfume oils or color additives. My stuff is clear. I wouldn't think the stabilizers are a problem but could be wrong. I also use it for cleaning my air cleaners.

Maxell and a few others sell a lens cleaning disk for about $20.00 probably available at Best Buy or similar store. The disk has a fine brush attached. You insert the disk as a normal CD, then run it for about 20 seconds.
Cheap, simple, safe and it works.
I agree with Theo.

Sony state quite clearly to their technicians in the two SACD Service Manuals I have (SCD-C333ES, SCD-XA777ES) that the only acceptable method is compressed air.

I have a rotel 855 that skips,do you think the compressed air might work or is player to old?
Myself, CD with physical brushes attached, and compressed air.

Not certain of isopropanol or any other solvent for that matter (I'd be concerned with the mount of the lens rather than hurting the lens itself, but a 99% USP grade isopropanol is also available at most drug stores; you just may have to ask for it.
Besides the cd with brushes or compressed air, try alcohol free liquid eye glass lens cleaner.
You're welcome, but 70% is not pure and I wouldn't trust their definition of "water" (yes I'm a cynic from way back :). Use what you want, but I have only ever used pure isopropyl (which you generally have to ask for) or pure acetone, which you can find on the shelf.

Good luck and hope you get it working right!
Danmyers...The distilation process used to make alcohol yields about 30 percent water. It boils off and condenses along with the alcohol. So the water is distilled, and you don't need to worry about it.
I wonder where username Elizabeth is. This seems like a good thread for him/her to weigh in on. I've noticed they often have some very useful insight on these kinds of issues.
Eldarford - I never worry about it 'cause I only buy pure :)

Me thinks you're talking about the process of making alcohol and I'm talking about the process of marketing alcohol. I buy pure to be assured there is no difference between the two.