Here is a "stream of consciousness", bits copied from posts over the years, most from photo.net a decade or two ago. They offer opinions which might not be totally correct or complete, but I offer them in the hope that they will be helpful.
<start of copied posts>
I had the same problem with the film start sensor in a very used SL66 film magazine I had purchased online. Having had a repair manual I was able to make the adjustment myself. It is not a very difficult procedure but the go/nogo specification of 0.30 mm /0.35 mm should be ignored as films and backings thicknesses have evolved over the years. A film backing with about 1 inch of film and the tape attached will make a good gage. This could be obtained by placing a scissor in the changing bag when unrolling the film for the developing spool. Simply cut the film 1 inch away from the tape. No image is exposed this close to the tape. I can email any pertinent images and text from the manual.
erwin_schaefer, Jan 17, 2016
==================================================
There is a simpler solution to the SL66 film start sensor problem. The adjustment instructions in the manual apply to the gap between the sensor and the removable film insert. One could reduce the gap by simply applying some tape either on the bottom of the insert or inside the bottom of the cassette where the insert rests to raise it closer to the sensor. Experimenting with various thicknesses of tape would do the trick. I see this as an emergency resolution but no disassembly would be necessary.
======================================================
When it works I just ignore it! I can't say how often exactly but it isn't a lot.
The "feeler" is a small diameter steel roller at the top of the magazine that sits just behind
the topmost plastic roller of the insert. If you remove the magazine from the camera and
open the magazine's back then look at the top of the interior with the insert still in place
you can see it. It's the bright steel reflecting the shape of the top roller. Note that the
insert has two rollers at that end.
If you have a bit of manual dexterity you can test if that feeler works. Remove the insert,
push in the cover probe -- it's on the right side about halfway up -- so that the
mechanism "thinks" the back is closed. Start turning the winding knob and (while still
turning) push gently up on that feeler roller (it should move toward you a little bit along
with a black metal reinforcing band just in front of the roller). That should prevent you
from turning the knob, if you can still turn it then it's a job for a good repair shop.
If the mechanism works, you might need to have the position of the insert adjusted, there
are two set screws at the bottom interior of the magazine that contact the insert's bottom
that do this job.
If you determine that you need to count the knob turns (instead of taking the back to a
shop), you will probably have to experiment on your own. From my past (misguided)
Hasselblad days, I seem to remember that there is a marked "start" line on every roll. You
will want to line that start line up with a feature of the insert so that your knob turning
positioning is consistent.
The SL66 is great camera, don't be discouraged by this little problem!
Gerald
==================================================================
I had this problem using Fuji Provia and Kodak Portra films and I guessed it was due to the
thin film and backing paper. I worked out a system which relies on a number of turns of
the advance knob to get the start of the film in the correct position.
Firstly I marked a dot on the knurled edge of the magazine film transport knob with some
paint.
I aligned the arrow mark on the backing paper so that it was at the top dead centre on the
feed spool when looking down on the film insert.
I closed the back and turned the knob four full turns, using the painted dot on the knob
for reference. The film is then in the correct positon for frame one.
Hope this helps.
nicholas_clarke, Feb 8, 2006
========================================
Hi,
I bought a (well) used SL66 on eBay and had the same problem with the first film I put through : I could wind it through entirely, the start of the film was not detected by the SL66. Not having any experience with an SL66 I thus took 12 shots... past the end of the film
Fortunately the problem only happened with the first film. I might have loaded the film just a little bit too roughly - I now turn the knob rather gently.
But just to make sure I counted the number of turns needed to get to film position one : it's about 4 and a half full turns IF you first load the film until you can see the arrows on the back paper.
Each time I load a film now I check the number of turns, but as I already mentioned the problem never reoccurred.
By the way I have two magazines, both either without serial number or with serials of magazine and inlay not matching. Never had a problem. I read somewhere that the inter-magazine tolerance was such that no problems should be expected, although you'll never read a Rollei statement saying (= guaranteeing = risk of claims) that this'll work.
Greetz,
Jan
=========================
Norman wood , jun 09, 2004; 12:46 p.m.
.... I have had problems with my sl66 backs, one needed a good clean as the graphite grease inside had dried out, the other needed the film thickness sensor roller adjusting. This is done by removing the leatherette on the right hand side top section of the 'back'. At the top right hand corner is a hole with a screw in it, turn this in small increments (1/2 a turn at most) one way or the other (it is a cam adjustment) to adjust the film feeler roller. Sorry I cannot remember which way to turn it to increase or decrease the rollers sensitivity. I did mine a long time ago due to it not locking the small wind on knob when loading thin film such as Ilford Delta. I dont think this info will help the back you have but it may be of some use to you in the future. Good luck and hope you enjoy using the sl66 it is a very well made piece of kit when all is well.Norm.
--------------------------------------------------------------------------------
