Issue with new ABL servo

I have been using a towerpro sg90 servo for ABL. the one I had had gotten a little flaky due to being crashed into the bed repeatedly as the ins and outs of the ABL firmware are getting settled. possibly some rounded off gear teeth. No big deal, cheap part.

I installed a new one and went to set the extend and retract angles. However, the new servo, although the same model and connected with the same three leads, is not behaving like the old one. I can't predictably return to degree settings. When I do get it to move, no matter which direction I give, it goes about 20 degrees further in the direction it was already going. Then, If I turn the printer off and on, it might be able to be moved in the opposite direction. Any ideas? I know there are some RC guys here. Thank you.

Probable cause - I tried a suggestion at the same time as the servo replacement of insulation the 5V terminal on the usb cable so that the boardset could be turned off with the overall power switch while the board was connected by and powered by usb. Seems to be back working now that that was changed back. I am going to post a note about this in the thread where that was suggested.

And for future readers, my response regarding a possible connection - http://3dprintboard.com/showthread.p...ll=1#post28854