Mamiya 65mm f4 L-A not firing on RZ67

Hi All,

I've been having an issue that I can't seem to get my head around.

For the last several months my 65mm f4 L-A lens for my RZ67 Pro II will fire only in mechanical mode 99% of the time. In regular manual mode firing the shutter will result in a beeping noise but no indicators in the prism (where you would normally see the darkslide warnings etc). The exception to this is that if I fire in mechanical mode I'm then able to take one fully manual shot before the beeping begins again on the subsequent attempt at a manual exposure.

The issue happens only with this lens. I've tried cleaning the electrical contacts on the body and lens with a 50% isopropyl alcohol solution. I've checked that the cable release socket on the lens is screwed completely in and the time exposure lever is set to the normal N position. I've also tested it with different film backs and the issue persists.

I'm open to any and all suggestions, as I'm pretty puzzled and people with intimate knowledge of this lens seem to be few and far between.

I've disassembled and reassembled multiple RZ lenses, electrically they are not overly complex, and pretty similar in how they work (from the electrical standpoint). There's nothing really unique about the 65 M/L-A in this regard. Did you try changing batteries in the camera? I'd start with that, even though it doesn't seem like that would be the case. It sounds like something may have shorted inside the lens itself, or is not returning the correct info to the camera.

Battery is brand new right out of the package, one of the first things I checked. Sorry I should have included that in the OP.