Oh I had to do a little of reopening the client and make it first run at 1,6 then I am able to overclock it to 2,2.
But there is one that do not want to work at 2,2 but at 2,1 yes.
Might it be my usb port that doesn't receive enough power ?
Because I have 3 block erupters and 2 antminers directly plug in my computer usb ports...
Thx Doc !!!
I don't have an U2 but afaik they are the same hardware as the U1's (which I have a bunch of). For me some couldn't go up to 2GH/s without throwing HW-errors in the 50% range. The problem is with the quality of the chip. Some need a little bit more voltage than others. So I think the only possibility for you to get all of them to 2,2GH/s is with a little voltage mod of the not so good performing ones. For me I only upped them about 0.08V but that did the trick. Your computers usb ports "should" be able to supply enough power or shut off completely I think.