Mamiya 7 150 shutter lag
My Mamiya 7 works great with the 43 and the 80, but the 150 doesn't shoot immediately when I click. Rather, it does nothing for about 4 seconds and then doesn't keep the shutter open for the given amount of time (it is probably shooting at the fastest speed possible, as I got very underexposed slides).
The contacts seem clean. Is there anything I can check/do before sending the lens for repair (and any suggestion of where to send it to)?