so, having wasted most of an afternoon, I am turning to the experts for help. Here's the setup: Toyo 45G, Symmar 150 5.6, PA-145 back loaded with FP3000B. First time to actually shoot with it. Subject is a beer can about 28" from the film plane, and lighting is from a RayFlash attached to Sunpak 30SR. Lens to subject about 18" I guess. Shutter at 1/200th - speeds not actually formally tested but sound about right. Having focused it and got the compo about right, first shot, looking at the print, it's way over exposed, with a vague image of the can. So dropped the power on the flash, and selected smallest aperture, which is F45. Print is still almost completely white. Then I noticed........the front panel in which the lensboard sits, was not mounted properly and had probably been leaking light. ha! Prints 3 and 4 were also duff, in the same way. Then a brainwave struck me.....I pulled #5 from the back without exposing it in the camera. It was also almost white. I got this batch of film from B&H, dated until December this year: although it came to me airmail and presumably got xrayed in the process. even so, I very much doubt there would be a problem with the film. 1. because film problems are quite uncommon, and 2. because the other togs who I shared the order with, also got instant film and have been using it, I would have heard about any film-related problems long before (we made our order back in Feb of this year). So I cut my losses and binned that pack that was in the PA-145. Got a fresh pack from the fridge, loaded it, pulled the black paper, then pulled the tab on #1. This time the print was black!!! Invigorated, I loaded the back into the camera, and made an exposure........the print was again almost white, with a faint image of the can. #3 I pulled the tab on, without loading into the camera, just to check, and sure enough the print is white again. So, where does the fault lie? I pulled the bellows out and couldn't see any obvious damage but, what is the most effective way of checking for pinholes? The only other thing I can think of, is the instant back doesn't seem to have the right type of darkslide. I looked at another PA-145 locally, and that one has a metal darkslide where my example has a d/s that seems to be made of fibre, rather like the Polaroid 405 backs. Carefully inspected the structure of the PA-145, and could not see any damage, and the dark slide is not cracked and is nice & flat. Any idea?