I managed to repair the aperture on one of these and holy moly that was hard work. To try get to the point quickly – i'm not sure how I specifically fixed it.
I disassembled it enough to remove the mirror box, shutter, and aperture control assembly from the mirror box. Then I cleaned the 3 electromagnet surfaces with an isopropanol slip of paper, after which I reassembled things mostly following steps in the
service manual available on archive.org
Then the rest of the camera was re-assembled, cleaning any contacts along the way with isopropanol. I'm skipping over alot of details... but in terms of what I did that could've fixed the aperture, the only 3 things I can think of are either:
1) the surfaces of the magnets were sticky with oil or something and not releasing (I read a post somewhere a while ago claiming this to be the common cause of fault).
2) some dirty contacts were causing issues.
3) something had jumped out of place or gotten misaligned, and was reset during the reassembly.
Either way I guess it is repairable, but we'll see if it lasts or if I caused any new problems I haven't noticed yet.
To go into more detail though: I think the camera wasn't as unpleasant to disassemble as it initially seemed... it was just time consuming. The service manual is pretty good with a step-by-step on how to reassemble most things (even if there's some guesswork from the awful scan quality) and gears that need to mesh together have markings to aid alignment. Some steps can still be fiddly but it didn't feel like there was a huge risk of breaking, bending, or losing alignment with parts as compared to other cameras. I could've taken more photos to keep track of where all the wires go though. Searching for teardown photos is how I found this thread!
The service manual suggests you don't need to remove the top PCB and as many parts as I did to remove the mirror box, but I was struggling to get the thing out since there was a little bit of adhesive sticking them together that felt like a screw i'd missed.
So the other major fault with these cameras seems to be the rubber buffers in the shutter turning to slime and fouling the curtains. I feel a fairly deep disassembly is maybe a good idea regardless of the state of the aperture.
The shutter was opened while it was cocked and the old bumpers were replaced with ones cut from 1mm rubber sheet. I got some scraps of the stuff from when a neighbor was having their roof repaired.
The tricky part of reassembling this was that one spring jumping out of place, and the best way I found to get that back in was leave the hook part disengaged when reassembling, then firing the shutter after putting the screws back in to move the hole closer to the edge for easier access, but it's still a bit of a fiddle.
The other problem I had with this camera was missing segments on the viewfinder LCD. The plan was to swap the part from a different camera (that has an IC failure, I think) but while cleaning the adhesive off of this one all the segments looked like they were working (they kinda activate from current from your body or something).
The only solvent I had that could remove that adhesive was acetone, but wiping the surface of the LCD started to dissolve the stuck on polarizing film so just keep it to the contacts.
It was reassembled with the bare cleaned gold pads in place and a 0.3mm thick strip of rubber placed on top of that, between the flex PCB and the metal retaining stuff, to try even the pressure out. I'd guess the original conductive adhesive was there to aid in assembly but I could easily be wrong. There's repair steps in the service manual but I didn't find them particularly clear.
Also I swapped the other LCD with a slightly better one from a spare camera but that wasn't too difficult.
But yeah after some gaffes with reassembly, like finding out i'd gotten the grey wire between that 3 layer stack of PCBs on the right, mangling the autofocus/ manual switch by assembling it in the wrong position, and battery corrosion in the handgrip having made the shutter button always on, I managed to get it back together with no screws left over. Now I gotta actually run some film through it.
Last year I bought that 2nd broken 9000AF to possibly use for spares, but mainly to disassemble it and see if it was possible to reach the aperture without messing up a bunch of adjustments. After getting the covers off I lost interest though... a mix of getting a fright with all the origami PCBs and feeling more excited about Prakticas at the time. Keeping track of screw locations by taping them to paper doodles is nice just for how you can shove it all in a box if you need a break.
After a year i'd forgotten the camera had deeper electronic faults, probably caused by leaked batteries, and was pretty excited spotting a spring that'd jumped off of its sear. Like it seemed a pretty blatant solution to the problem... and it wasn't till I saw that blinking F-- error again after careful reassembly over a couple days that I remembered. But it might suggest multiple causes of aperture failures besides the sticky magnets.
But yeah, I'm pretty excited to now have a working one of these stupid lumps – they're cool cameras! Or rather, i'm excited to know these common faults are repairable. I was pacing around last year considering spending more money than I had on a confirmed working one, but knowing that it'd be at risk of turning into a pumpkin at any moment I figured i'd never feel like I truly owned it or could rely on it unless it was something I could keep working.
