Hi Dr Funk,
I have a DJM-700 which I have owned for around two years now and I have the same problem in that I am only able to select certain effects.
Mine appears to be an intermittent problem as one day out of the blue my FX section had full functionality but once again returned to it's faulty condition the next time the mixer was powered on. On other occasions I was able to access some more of the FX than others but I have never had full functionality since.
While doing some research I found a thread with another DJM-700 user who was experiencing the same problem. He said that he took the faceplate off his mixer to give it a clean and have a poke around and this inadvertently fixed the problem. Just yesterday I attempted to do the same but to no avail. I called an authorized Pioneer service center today and spoke to him about this and he said that if the FX selector pot has become worn that it would likely be the cause of this problem and would cost around $90 to replace.
I have had my mixer for approximately two years now and if it's any consolation I also began having this issue about a month or two outside of the warranty period. I have just ignored the problem up until now because I found it easier to focus on beatmatching and inspired me to become much more adventurous and creative in my mixing style.
However I have also partially lost functionality of my crossfader as for some reason unbeknownst to me my crossfader assignment is also faulty (i.e. fader one always plays through regardless of crossfader assign switch setting, fader two and three work on side A and B respectively but play through when sides are reversed and fader four works on side B only. Unfortunately I did not realize this until after I had already gone and bought a replacement crossfader :(
I wonder if you have a similar problem as I am hoping that this is somehow linked to the FX selection problem but I am doubtful of this and fear it may mean replacing the main board which I would assume will be quite expensive.