Bronica ETRSi Mirror up fault...

Greetings! and thanks for any help.

I have two lenses for the ETRSI, a PE 75mm f/2.8 and a PE 150mm f/3.5. The mirror up shutter release seems to work properly on the 150mm but does not on the 75mm. There is the snick of the shutter firing but no apparent apperture motion and frames exposed with mirror up are blank. I read elsewhere on this site after a Google search that these shutters are mechanically activated but electronically timed. So it seems to be a problem with the lens.

So the question is: what, if anything, can I check or clean or tweak on the 75mm to try to get the electronic timing functionality to work? I'm hoping it's a swab or dust removal type fix but am afraid it's a deeper problem.

Any info you can pass along would be a great help.
Thanks! ...edN

Your question is hard to parse, it's not clear if you are talking about the mirror lock up lever, the shutter release, or something that happens only when firing the shutter with MLU engaged.

The mirror lock up should be pretty independent of the shutter release. You turn the MLU lever and the mirror flips up and lens shutter closes. Then you fire the shutter with the usual button or cable. The shutter is electronically timed whether or not the MLU lever is engaged.

You can test the lenses and camera without film by engaging the multi-exposure lever, so that you can "wind" and cock the shutter, and see what it's doing when you fire. Try that. Try firing the shutter with and without the MLU lever engaged. You should see the lens stop down to the taking aperture, shutter open and close. Then when you wind it opens again. If you try this without a battery, each lens should open for 1/500. If the lens shutter never opens at all when fired, then the problem is in the lens shutter, but it's deeper than simply the electronic timing.