OK guys I'm back with pictures and more info, I appreciate all the help so far I have been reading night and day about mosfets and driving them I now have a pretty good understanding of them I see where you could pull your hair out trying to get everything just right.
So to get up to date on what I have done. Both the boards x and y had some shorted mosfets all three legs were shorted together on 3 mosfets on the x board I'm just going to focus on that board for now.
So I ordered the Fairchild mosfets that ronv posted I sat down and compared all the specs read all I could about what they mean I think I could make the call myself in the future thanks for pointing me in the right direction there are lots of choices out there.
I replaced all eight fets it went well came out nice, reinstalled the board same thing the stepper motors just shake when trying to move they would move if you helped them along. (I want to add that the problem is not external to the board works fine with boards from other machine).
Removed board for further inspection I'll post some pics at this point so you can see what I'm working on might help.
here it is the top side you can see the mosfets I replaced, also everything on the board past the row of transformers seems to be logic and it has diagnostics that say its working OK.
does that make sense? If so The first transistor (Q26 in above photo)in all eight gate drives is shorted base to collector what could cause this? I verified by desoldering one end on a few of them to make sure I was not testing through another part of the circuit they were still shorted showing 0 resistance either direction on ohm meter and no voltage drop either way using diode check function the second and the last transistor in the drive check as you would expect but again all 8 first transistors shorted base to collector. could the board still work like this? but have a weak gate drive? maybe this is what was killing the mosfets? so many questions I just don't see 8 transistors all failing at exactly the same time.
So far it looks as if I need at least 8 transistors and one optocoupler to get this board working. still confused about this transistors I guess it would just loose one stage and the optocoupler would be directly driving the second transistor through the first? and still maybe work dose that sound plausible?
Trying to understand how I could loose 8 transistors and 3 fets and a optocoupler in my head transistors died off over months maybe years causing a weak gate drive, that put strain on the fets until they failed, the shorted fet took out the optocoupler what do you guys think of that scenario?
Sorry for the long post I guess my main questions are am I on the right track, do you think I have correctly id the failed components, and could all those transistors be bad and the board still work? for a while.
Thanks for all the help
Jeff