Here is what I did to set backfocus on our HM700. I set my focus chart about 20 feet away and hit it with a 1k. Zoom in to the chart and set my focus until image is sharp. (You may have screwed yours up so bad that it may not get sharp. In that case use a tapemeasure and set focus like an AC on a film camera. 20feet from the film plane and 20ft. on the lens) Zoom all the way out and loosen the backfocus set screw and adjust until image is in focus and sharp. Do this a couple of times until you’ve got is dialed. Then I went outside and did it again on something really far away. Works like a charm.
Also, every time I remove the lens I check backfocus. I think it’s a good idea to check backfocus at least every month or so.
Hope this helps.
cheers
Kevin