I attempted to repair a Nikon F100 film camera sold for-parts. Unfortunately, for lack of documentation and knowledge I created a lot more work for myself than was necessary. Here is what I wish I knew before starting.

The body worked fine for a few weeks but now something more has gone wrong: after a few moments powered on, the camera becomes unresponsive and cannot be turned off or restored until the batteries are reinstalled. Film rewind and advance have also stopped working. Film detection is fine, showing an error when film is loaded. The shutter and focus screw drive work fine too.

• It isn't because of weak batteries, since the issue persists with a bench power supply.
• It isn't a button comms issue since none of the buttons anywhere on the body work.
• It isn't a mechanical issue since supplying the motors with power electrically isolated from the body runs the mechanisms fine.
• It isn't cleanable corrosion on the power FPC: I removed, thoroughly cleaned, and reinstalled it with no improvement. This involved soldering and taking off the center assembly, film advance motor, and solenoid assembly. It sounds scary but is really not too bad, not beyond the scope of what's described below.

I speculate without evidence that the whole power FPC and possibly the DC-DC converter on the bottom plate have failed in some subtle way, sporadically hanging the CPU. On the outset my goal should have been to just replace the entire power FPC with one from a donor (or at least to just remove the power FPC and observe it really thoroughly), but at this point this is too much of a time investment for me. Good luck with your repairs.

The Nikon F100 repair manual and parts list are necessary but not sufficient. They are terse, vague and narrow in scope. Copies circulating online are low-quality scans. Afotandovy has some useful disassembly photographs and comments: https://afotandovoy.blogspot.com/2013/02/reparacion-nikon-f100.html

If I could go back in time I would urge several points to past-me:

• Read Richard Haw’s brief general camera repair fundamentals articles https://richardhaw.com/lens-camera-repair-fundamentals/ Forcing things when I should have taken a break led to unnecessary damage that was difficult to repair
• Almost the instant you take off each tiny screw you will drop it on the floor and forget the hole it came out of. 
Come up with some system to defend against these things. 
Many of the screws look near-identical and almost none of them are interchangeable. 
Pill tray systems will get knocked over and you will mix up the compartments. 
I should have disassembled everything over a magnetic screw mat, and sorted screws according to their names from the repair manual.
• If I had known how annoying everything was to clean before reassembly I would have worn disposable gloves for everything.

• JIS 0 screwdrivers. iFixIt Minnow has JIS-compatible ones.
• Fine tweezers
• Rocket blower
• Cleaning materials:
  • Coffee filters
  • Microfibre cloth
  • Toothpicks and Q-tips
• Cleaning chemicals:
  • Distilled water
  • 99% Isopropyl alcohol (limit using on the internal plastic as it gets brittle)
  • White vinegar (not for use on the plastic but rather for cleaning rust for metal parts that were removed from it)
  • Acetone (turns the internal body's "PC-GF20.AL" plastic into mush instantly on contact. Essentially destructive. Extremely limited applicability if any here. Only thing I’d use it for is as a last resort for extremely tight screws, applied with a toothpick)
• Strong double-sided tape. I used Scotch 9495LE.
• Soldering iron (to get some delicate ground wires off without damage)
• Box of 100 nitride gloves

A lot of for-parts F100s on sale already have some essential components gutted. This makes the economics of repairing them pretty bad. Here are common missing parts I noticed, together with their replacement status:

• Eyepiece
  • The standard is Nikon Viewfinder Eyepiece 2927. Ebay price is $25.
  • It is a very simple part. Metal aftermarket versions are currently manufactured and cost $12 shipped.
  • The ring for the F100 seems to have dimensions close or identical to the Nikon DK-17 (for which free replacement models are published), but I haven’t yet found empirical evidence they are interchangeable. You’d still need to find a glass window for those too.
• Battery cartridge
  • The standard is Nikon MS-12 (4xAA batteries). Ebay price exceeds $100 which is obscene.
  • Bogdanbogvzyan sells compatible design files for $10 at Cults3D: https://cults3d.com/en/3d-model/gadget/nikon-ms-12-aa-battery-holder-for-f100 . 3D prints of that can be found for $30 shipped. See "## Experience with 3D-printed cartridges" section below.
• Focus screen
  • The standard is Nikon Type B Focusing Screen 2599. Ebay price is $28.
  • There are actually aftermarket screens (with split prism!) with correct dimensions on aliexpress: "Dual 45 degree Split Image Focus Focusing Screen for Nikon D1 D1H D1X F100 PR129"
  • Richard Haw has described cutting down and shimming an existing focus screen of a different model. I don’t know why ground glass of the right thickness wouldn’t work OK. Dimensions in Figure 1.
• Film door
  • The assembly is 1B999-938 in the parts list. Replacements sell for $100 which is obscene.
  • The latch hooks frequently fail and a simple repair jig + metal hook kit can be bought for $20 which seems reasonable.
  • The whole film door is actually a simple passive electromechanical part that would be feasible (if a bit complex) to fully remanufacture, if/when it becomes economical to do so. I don’t have the expertise to do this, though.

My broken F100 came without the eyepiece and its battery cartridge was shattered. The seller said this camera died from battery corrosion. By the time they cleaned the battery compartment the corrosion had already corrupted the inside of the camera. Its behavior was erratic:

1. Typically the camera would appear totally dead. The batteries would sometimes heat up quickly. Sometimes putting batteries in, the LCD would show garbage, sometimes fading out.
2. Rarely the camera would turn on and show the low battery LCD symbol. No function or button worked in this state. If you pushed any button here the symbol would start blinking.
3. Very rarely inserting the batteries would power up the camera into an ostensibly-working state for a minute or so. Here the shutter would behave like it was being held down forever after its first press, until a power-cycle.

The top cover, baseplate and grip had to be removed to expose the contaminants that had leaked into the body. I followed the “Disassembly 1. Exterior" section of the F100 repair manual. Also helpful are the afotandovy photographs up to and not including removal of the LCD screen’s screws.

Fine points of disassembly:

• There is a FPC (Flexible Printed Circuit) connecting the top cover to the camera body under the side opposite the LCD. It is easy to rip if you don’t know it’s there. To remove the top cover safely I lifted it off lift it off as pictured in Figure 2. You have to lift the cover off with one hand and unscrew the two retainer screws with the other. See page A-30 of the repair manual.
• The metal grip/battery compartment is electrically grounded with a copper clip retained by one of the screws. See "Grip" on page D-13 of the repair manual. A blue wire is soldered onto that clip, leading into to some FPC inside the body. I desoldered it to avoid the wire snapping during handling. The wire and clip is visible in Figure 3, circled in white.

Corrosion cleanup for all the electronics followed the same pattern:

• Flaked off what corrosion I could see with a toothpick
• Wiped with water to dissolve the rest of the corrosion
• Final wipe with isopropyl alcohol
• all the while blasting air at it with a rocket blower

The symptoms were likely caused by contamination:

• There was crud around the power FPC ribbon. Something around here was the plausibly cause for symptom 1. See Figure 4, red arrow.
• A window at the ceiling of the battery compartment exposes a spring-loaded "battery indication contact." Normally a peg on the MS-12 battery cartridge displaces the contact to open the switch, and unless that switch is held open then nothing will work. See the "## Behavior at various voltages" section below. A plausible explanation for symptom 2 is that corrosion interfered with this opening.
• Buttons on the top cover signal depression to the body by shorting a radial pad on the FPC to a ground rail. Symptom 3 was due to contaminants shorting the shutter switch closed around some contact arms. See Figures 5a and 5b.

Separately, removing the metal grip revealed rust-red corrosion that I cleaned off with white vinegar, rinsing thoroughly with water afterwards.

...and then everything is supposed to go back on the way it came off. The grip rubber and diopter cover need new double-sided tape. It could’ve been that simple...

During disassembly I stripped the head of a stuck screw. Richard Haw, linked above, has advice on this. I managed to remove it with a dot of white vinegar and a lot of friction through a flathead screwdriver.

Of course you don’t know what screw you need until it is lost or destroyed. If you are lucky the screw is one that came in a pair so a twin is available for measurements. One way to measure a machine screws is to paint it in ink with a ballpoint pen and take a print of it on ruled paper (rules are often 6.35mm apart). A picture of the print provides thread pitch, length and diameter via the ruler tool in Gimp or Inkscape. See Figure 6.

Sometimes you can cross-reference the F100 repair manual to a parts list to find the screw name. For example CKT #778 appears on page D-1 of the repair manual, and in the parts list it has Part No. B1-14030FD indicating it is some 3.0mm-length M1.4 screw. Not all the screws are named like this.

The film door’s focus-selector D-pad popped off during cleaning. That button is mechanically attached to the film door by a collar that’s pressed on from the inside of the door. It’s impossible to reattach without disassembling the door. Avoid this situation. It isn’t fun…

This is an obscure repair, I can’t find anyone doing it. Actually there is a nice explosion diagram of it on Page D-26 of the F100 assembly manual (“rear cover"). The delicate part is lifting the internal black panel off the rear cover. Figure 7 shows the backside of what you must lift off.

• Like the top cover FPC, the area of the FPC near the focus area selector dial area is screwed down and you will rip it if you don’t know it’s there. As you lift it off you have to unscrew a screw normally holding the FPC at the red arrow in Figure 7.
• The FPC on the panel is tacked to the cover’s body with two pieces of double-sided tape (white arrows in Figure 7). The tape can be loosened with a toothpick saturated with isopropyl alcohol.

For reassembly the only delicate part is getting the focus area selector dial back into place. Tape the dial on from the outside during reassembly so that it stays in place temporarily. Then as you are lowering the internal panel back in place, you can screw the sliding contact pin assembly that sits over the FPC back into the dial.

Negligently, I failed to notice an obvious screw on the battery compartment while removing the baseplate and I ripped it off, taking most of its boss along with it. I should not have used so much force, should have paid closer attention to the repair manual’s exploded diagrams and counted screws more. My approach was to replace it with a similarly shaped M1.6 screw and a brass heat insert encased in epoxy.

I carved away a segment of the shattered boss so the brass heat-insert could be brought nearly into position in free space:

Then I used the baseplate as a jig. With the baseplate+screw+insert set on the body I held a soldering iron on the screwhead at 380 C, which eventually softened the plastic enough for the baseplate to set the insert into position.

Finally I used a toothpick to coat the partially-mounted insert and surrounding area with epoxy. I quickly reinstalled the baseplate+screw before letting the epoxy set. Gorilla Ultimate epoxy is one of the most foul things I have smelled in my life. Do this outside!

This ordeal took two tries to get right: in the first try I tried to eyeball the insert position without the baseplate as a jig. Although position seemed OK to the eye, in reality it was poor enough that trying to reassemble it sheared off the head of my screw.

The F100's behavior depends heavily on some internal capacitive state which makes precise/"steady-state" measurement of these thresholds tedious and out of scope. In the repair manual A-31 and R-5 list relevant voltage ranges I sought to observe.

• LCD and everything remains totally dead when the battery indication contact (Battery Identification SW0 on page E-16 of the repair manual) is left untouched, as high as I tested up to 6.0 V.
• With the battery indication contact displaced:
  • The LCD comes alive at 3.3 V and up. At 3.3 V I could turn my camera on.
  • Blinking battery LCD symbol with no functionality from 3.3 to 4.0 V any time you push a button. Button presses spike current draw from < 1 mA to 290 mA.
  • The shutter will fire from as low as 4.1 V, though whether it fires seems to depend a lot on the state of some internal capacitance(?). Raising the supply from 4.0 to 4.1 V the shutter will not fire, but starting the camera cold at 4.1 V seems to consistently allow the shutter to fire. Shutter actuations spike current to 820 mA.
  • Full battery LCD symbol seems to consistently shows when the camera has recently been supplied above 5.0 V.
• When the battery indication contact is released while the camera is supplied 5.0 V, behavior becomes erratic. The camera dies a few seconds later. The LCD dies first and other functions follow soon after.

The MB-15 6xAA battery grip has a second peg in addition to the one on the MS-12 and MS-13. (Battery Identification SW1 on page E-16 of the repair manual).

I attempted to print Bogdanbogvzyan's design linked above with PLA (Thank you HackManhattan). The print was vertical as the designer suggests. This print failed during assembly due to layer separation and the screws sheared out of their holes.

Next I ordered a CraftCloud print in PA-12 nylon. It is fragile: the top cap bows out against the batteries' spring pressure. My print's peg doesn't reliably displace the all-important battery indication contact (See "## Behavior at various voltages"). Not wanting to deal with this anymore I taped some insulation in place under the battery indication contact to semipermanently hold it open. See Figure 13.

In the early 2000s Leo Bodnar did some fascinating work on the F90X:

• https://geocities.ws/leobodnar/F90X_rewind.html
• https://geocities.ws/leobodnar/f90secrets.html

Pads near the DX reading pins have an undocumented serial line that let you overwrite EEPROM registers. Leo succeeded in writing to a register on an F90x that controls how much of the film leader the rewind operation leaves exposed. Unfortunately the zips on that page are not available anymore. They likely would have described the serial interface.

The interface may be the same as the one on the 10-pin connector, which does have known, surviving implementations. F100 manual’s EEPROM register table suspiciously names a “FILM TONGUE" register at 0x0081 for “Ver 4.XX" and at 0x006E for “Ver 5.XX"… there is also a “CHECK SUM" register which may need handling too.

On the outset a successful repair seemed too hard and low-likelihood. Looking back I think it only seemed so because of poor information availability. Finding obscure technical information is pretty miserable in the age of AI. Google hasn’t worked right since before covid. Its replacement, Claude, always tells me I’m a dangerous incompetent who should give up on everything and call 988. Sometimes through its ugly condescension Claude accidentally leaks useful information and who it learned from. Sadly I think this will be patched soon.

Forums, especially Reddit, are virtually exclusively populated by deeply low-rent people. The Redditor is a uniquely brittle, ignorant, over-socialized, navel-gazing, low-agency creature. If you do anything outside its very limited script of interactions (e.g. seek or provide novel information) they will seize up and start shrieking like at the end of Body Snatchers (1978). The small, over-moderated ‘specialist sub-Reddits,’ the ones everyone’s always insisting are different, are equally if not more bad. If you use Reddit that is embarrassing and you are a bad person.