Won't pick up bobbin

We have some old Happy machines, and we have the same problem on a couple of heads. When there is a thread cut, the needle will NOT pick up the bobbin consistently. It seems to happen on all needles. This doesn't occur every time, but seems to about 1/2 of the time. It seems to do better when it is run slower after a thread cut, and it also seems to occur less when the fabrick is thicker or if it is sewing in an area where there is a lot of stitching already. Here is what I have tried:

1) Set hook timing

2) Set needle depth

3) Adjusted bobbin tension and thread tension.

4) Adjusted cutting knife.

5) On the HCA machine I've gone into the software to increase the # of stitches it goes slow before speeding up, and tried to adjust the thread cut to be long.

I'm running out of ideas, does anyone have any suggestions?

Thanks,

Chris

hi im brian, im an embroidery machine tech....is there a thread retainer under the knife when its in the home position it should trap and hold the bobbin thread after trimming.
also if you can move the stationary knife a little further away from the bobbin case it will help a little. one more thing, remove the moving blade and polish the outer edge as sometimes these get nicked and snip the thread short with the rough edge rather than the cutting side.

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