I have a DC07 which kept on getting clogged with dust collecting in the top, coloured part of the cyclone.
Basically, if you take the cyclone off the bin, you should be able to see up from the bottom all the way to the top thru the centre column - a torch is handy.
I ended up taking the screws (Torx screws) out of the top lid of the cyclone and looking inside. This is a complete pig of a job as you have to fiiddle with the lid release mechanism to get it off and fiddle even more to get it back on. The top was absolutely full of dust & dog hairs!
You can't take the cyclone apart any more than that - the top half is bonded to the bottom, not screwed.
I contacted Dyson, got hold of someone technical and explained the problem. I pointed out that Dyson state categorically in their adverts that their machines don't clog.
Despite the machine being out of warranty Dyson sent a new cyclone, which had had a small design change in the area of the vortex tubes.
It's also worth mentioning that Dyson offer fixed price servicing of £65 including all parts and labour, done in your home and with a years warranty. When our motor packed up, the cost of a new motor and filter was £60. Dyson did the job for £65 PLUS fitted a load more bits that were beginning to wear. I ended up with about £120 worth of bits for my money.
Did that help?
John, March 2008