Did you carefully check whether any of the pins that engage with the cam is bent? Or perhaps the timing assembly in the shutter unit may be forced to damage... or some sort of mechanical interference to the unit. It's hard to tell unless I have it in front of me and carefully play with the mechanism with a pair of tweezers.

In the worst case you may have to replace the shutter's timing assembly. I think I have one of Yashica TLRs that can be cannibalized.