Need help with my Yashica TLR!

[syaobai]

I've just gotten a new Yashica Mat 124G but I have problems and I dunno how to fix it...
I have tried it with a few rolls of 120 film and was able to get it to work, but the crank keeps jamming after taking 5-7 shots. Anyone knows the reason for the jam because I'm pretty sure I did the winding and rewinding properly.. and how do I fix this?

Thanks!

 

[zenesh]

Some gear might be slipping in the mechanism.

Same thing happened to my yashicamat. Jam after a few shots

Brought it to "de camera consultant", Mr Phillip Tay and he tinkered around in the mechanism, and replaced a shim. 1 gear was slipping as the film was wound up.