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Failure to cock the shutter with the lens panel racked out from infinity is quite likely due to accumulated wear in the shutter cocking linkages. There is an adjuster to rectify this problem but it requires disassembly of the film winding crank and side panel to gain access. With the panel off, taking care not to lose some un-anchored small parts, focus knob set to infinity, a lock screw and adjustment collar is accessible through a hole in the wind crank mounting plate. Slackening the lock screw and nudging the notched collar by its edges clockwise with a screwdriver tip will tighten up the cocking action but must not be overtightened. This is a DIY job strictly for persons with experience of precision mechanical repairs.

Just some thoughts on this topic for future reference. I disassembled a Canon FDn 300mm f4 IF lens for aperture diaphragm cleaning. Its construction is very similar if not identical to my FDn 200mm f2.8 IF lens so it could be assumed the tear-down procedure is the same. This would apply to gaining access to the lens elements in front of the diaphragm assembly. The rear elements are part of the internal focusing mechanism and should not be tampered with. There are two sections of the lens barrel containing lens elements in front of the focus ring. The front section with built in hood unscrews after loosening three tiny grub screws visible once the hood is slipped forward, this contains the large front elements. The mid section which has a narrow sharp taper, unscrews after slackening off three tiny grub screws under the front of the focus ring. These are accessed by sliding back the rubber grip, rotating the ring until six slotted grub screws are visible in the three oval cutouts. The frontmost three screws lock the mid section in place therefore need to be fully loosened, the rearmost screws hold the diaphragm unit in place. The hard part was unscrewing these lens barrel sections as considerable turning torque was needed to release the threads. The front part came away eventually using rubber gloves for grip, but the mid section proved to be a real trial requiring various experiments with clamping the mid section and rear barrel plus using a heat gun at temps of up to 100 degrees celcius.

Just a follow up for future reference. I disassembled a 24mm f2.8 FDn lens for cleaning and found that the plastic nameplate ring was screwed in but no amount of turning with a variety of friction devices would release it. This was due to adhesive having been use under the ring to prevent it coming loose. My solution was to pry it off since the plastic is slightly flexible and could stand distortion. I used a thin guitar pick (plectrum) slipped between the lens surface and ring then worked it around the circumference to lift it slightly followed by a small screwdriver tip to pry it upwards. The lens surface was protected by small pieces of card (very important). Other FD lenses differ in the way the ring is held. The 28mm f2 FDn lens has a metal screw in ring which unscrews with enough friction applied. The 100mm f2.8 FDn has a plastic clip-on ring which needs to be pried off.

<p>Hi, anybody have experience of disassembling a Canon FD 300mm f4 lens for cleaning. I acquired one of these lenses with the aperture stuck wide open presumably due to oil migration onto the diaphragm blades. No amount of shaking or working the aperture ring will loosen it up.<br> I have successfully stripped down 100mm and 28mm FD lenses for internal cleaning, working in from the front. However the 300mm seems very different in construction. The front element drops out after unscrewing the retaining ring, but underneath that there is no further ring or retainer to remove. The front part of the lens barrel forward of the focusing ring has three small grub screws which I have loosened in the hope that this part unscrews together with the front lens block, but despite using a strap wrench there is no sign of it budging.<br> Any suggestions will be greatly appreciated!<br> Kokon</p>

<p>Just adding my experiences with the Nikon F3. I bought mine new about 30 years ago and it worked reliably on all my profesional work for nearly 20 years, then suddenly failed to power up. I simply packed it away assuming that its 1980's electronics had given up.<br> Couple of years ago my passion for shooting black and white film was re-awakened so I thought the F3 might be worth trying again. Put new batteries in to discover it would intermittently power up the metering circuit and fire the shutter using the shutter release button mounted on top. Obtaining a copy of the service manual it was apparent that depressing the shutter button closes two switches, first of which powers up the lcd and meter circuits then the second triggers the shutter electromagnet. Assuming that the switch contacts were contaminated I removed the top right handside cover (which required special tools to be fabricated) and sprayed aerosol switch cleaner into the compartment beneath the shutter button. The switches are buried beneath layers of components which look too complicated to disassemble. I also wiped clean the battery compartment and batteries with isopropyl alchohol. The result was same as before, lcd would show shutter speed and + & - indicators in manual mode, shutter would fire at correct speed, would consistently repeat this cycle multiple times then go completely dead. I repeated this process two more times, with last actually flooding the switch area with alchohol from a syringe. The camera would operate normally for many shutter firings giving me the confidence to try with film loaded but annoyingly went dead halfway through a roll.<br> Afer re-reading this thread I thought a more aggresive cleaning of the battery compartment might do the trick. I used an abrasive fibre glass eraser pen to rub the interior spring contact, threads of the battery cover and threads of the battery well, also inside of the battery cover, finishing off with liberal doses of IPA on a Qtip. Voila! the camera now works reliably.<br> The issue is certainly poor continuity in the battery circuit and also the F3 is very voltage sensitive. The batteries ground (-) through the battery cover and in turn through the camera baseplate and the slightest oxidation of the different metal surfaces could be the cause. Half exhausted batteries showing 1.35-1.4 volts each will not work reliably in the F3 but will happily power a different electronic slr camera I own.</p>