I found this SRT 101in a rather bad shape and after a basic cleaning had a look at it. While firing, the mirror stopped anywhere between right top and in between. After fiddling with many releases and the mirror lockup switch, it finally works normally. Now the next thing is it only fires on B or at one speed which seems to be always the same no matter which speed I set on the dial (1/60 ?). Can someone please explain ? Thank you.