A low value resistor connected in series with the fan can be used to measure the current flowing through it. The voltage across the resistor, therefore the current, can be calculated using Ohm's law.
Each fan will need to have its own current sensing resistor.
What do you mean by internal detection?
You could measure the current through the fan motors and if it's too high or too low, it's a reasonable indication that the fan isn't working properly. It's not as reliable as monitoring the air speed but it's better than nothing.
Which schematic are you building? The link on the first post in this huge topic refers to a 50V PSU and the schematic is very fuzzy and unclear. I take it you're building a different one?
If an AC signal is applied to either of those circuits, the capacitor will just charge up, then no current will flow, except that due to the diode reverse leakage and capacitance.
The new forum software has brought with it a few problems. Lots of the old posts, threads and attachments have gone and some users have experienced difficulty uploading attachments.
http://electronics-lab.com/community/index.php?/topic/41121-about-file-uploading/&page=2#comment-157554...
Of course the TDA7297 is not too small to fit on a PCB. Any IC can be mounted on a PCB, no matter how small.
I think what he's saying is it's not the right shape to fit on a breadboard or stripboard. For a start don't even consider trying with breadboard, which isn't suitable as the current is...
Did you upload your avatar from your hard drive or somewhere else on the Internet?
Usually I'd advise you install all the relevant updates for your browser and operating system but I'm able to post attachments from my work's PC which is running an old version of Firefox.
If you're still having problems with attachments, you could upload the schematic to another imaging hosting service and post a link to it here.
http://tinypic.com/index.php