Nikon F4 - Body not 'seeing' / recognising CPU lens - Sometimes.. ! Help?

NeillRobinson · Feb 4, 2024

Hey guys,

So I have a new-to-me Nikon F4 which seems to be working really great, apart from one small issue.. sometimes it can "see" that it has an AF lens attached, but most of the time, it can't.
I have tried cleaning the contacts with contact cleaner, with isopropyl alcohol, with an eraser.. I'm pretty confident the contacts are super clean. I've also tried a few different AF-D lenses, same behaviour. Those lenses are known to work on a DSLR so I would say the lenses are "known good" and the problem is defo with the body.

When it's working, I put it in S mode and I see the "S" in the viewfinder, and everything works as expected, I get AF, and it's pretty snappy! When it's not, I put it in S mode (or P, or Ph) and I see "A" in the viewfinder - this is expected behaviour when you select that mode but don't have a CPU lens attached. AF will then not work in any way - S, C, or in any drive mode, S, Ch, Cl, Cs.

I did think for a while that it was a direct correlation between cleaning the contacts and it working for a few hours, then not working again - I had that happen a few times and I thought hmm maybe the contacts are somehow oxidising really fast? But it seems that was just conflation - that I'd clean it and it'd work again for a few hours, until I put the camera down for a bit and came back to it, then the AF wouldn't work again. But now it's not working and cleaning the contacts again isn't making it work again.

It's not the end of the world because I got it for a good price and I don't mind using manual focus - all my other nikon film bodies are MF only - but it would be nice if it could be made to work!

Open to any suggestions on what the problem should be or how I should start to go about getting it fixed?

Thank you for reading and for any advice

Andreas Thaler · Feb 4, 2024

Thanks for the detailed report, as an F4 owner I feel for you

Since cleaning the contacts obviously makes an improvement, one option would be to polish their surface. It may be possible to remove any contamination that does not respond to solvents. Maybe you have a Dremel with a rubber polishing tip or very fine sandpaper.

Then you could see if the camera behaves differently when you change its position. That would be an indication of a loose contact point.

Andreas Thaler · Feb 4, 2024

In any case, I would also check the batteries and the contacts in the battery handle. If the power supply is not perfect, the cameras often go crazy.

Andreas Thaler · Feb 4, 2024

It would also be good to move all the switches and buttons to address any contact problems caused by oxidation.

I know these are the usual suspects on the checklist, but you have to do it.

Andreas Thaler · Feb 4, 2024

I'm looking at this now on my F4, maybe I'll think of something else.

Can you post a photo of the contact bar in the mirror box here?

NeillRobinson · Feb 4, 2024

Hi Andreas - I'll post a picture when I have the camera infront of me, I don't at the moment but give me a couple of hours. I have tried using switch/contact cleaner on all the other switches and buttons, but I could try again? Overall all the contacts look good in the battery compartments but I can check and reclean those if you think it's likely they're causing the issue?

chriscrawfordphoto · Feb 4, 2024

I would return the camera if you can. Repairs on the F4 are not cheap, it is a complex camera, and there are no new parts available for them.

NeillRobinson · Feb 4, 2024

chriscrawfordphoto said:
I would return the camera if you can. Repairs on the F4 are not cheap, it is a complex camera, and there are no new parts available for them.

Perhaps. But I paid £45 for it, including delivery. £45 for a "manual focus" F4 isn't terrible at all! Just the fact that there's an intermittant fault makes me wonder if I can fix it easily... I really think it's likely oxidisation somewhere - I know prior to me, the last owner was a professional photojournalist who passed away, his wife/widow then had the camera in storage for a long time and only wanted to start selling things recently. So I think it was likely working when put away, and has since just suffered as a result of being 'sat' somewhere..

Andreas Thaler · Feb 4, 2024

I've looked in my technical documents to see if I can find anything about this.

Unfortunately I don't see any troubleshooting instructions in the Nikon Service Manual for the F4 that could help.

In the SPT Journal January/February 1993, which is entirely dedicated to the F4, there is a note that in the event of AF problems, the AF connector under the base plate can be cleaned. It's just that it's too vague a hint for me to work my way through it based on luck.

Andreas Thaler · Feb 4, 2024

NeillRobinson said:
Perhaps. But I paid £45 for it, including delivery. £45 for a "manual focus" F4 isn't terrible at all! Just the fact that there's an intermittant fault makes me wonder if I can fix it easily... I really think it's likely oxidisation somewhere - I know prior to me, the last owner was a professional photojournalist who passed away, his wife/widow then had the camera in storage for a long time and only wanted to start selling things recently. So I think it was likely working when put away, and has since just suffered as a result of being 'sat' somewhere..

I agree with that.

Andreas Thaler · Feb 4, 2024

NeillRobinson said:
Hi Andreas - I'll post a picture when I have the camera infront of me, I don't at the moment but give me a couple of hours. I have tried using switch/contact cleaner on all the other switches and buttons, but I could try again? Overall all the contacts look good in the battery compartments but I can check and reclean those if you think it's likely they're causing the issue?

It can't hurt to clean everything again or carefully polish the contacts if accessible.

Perhaps one of the pressure springs in the battery compartment is corroded by battery acid and there are problems there. It's best to check with a magnifying glass.

Kino · Feb 4, 2024

Take great care in removing any pin-style lens bridge in the mount.

I took one off a Pentax 645 and it nearly drove me insane getting back in; microscopic springs and tiny gold plated contacts are no fun to wrestle!

Andreas Thaler · Feb 4, 2024

The contact block may not be screwed completely tight at the top of the mirror box, but you can't get to the screws directly. It could help to remove the bayonet ring. If you can loosen the screws.

But be careful, there are some couplings underneath and the ring for the aperture simulator runs against a spring. Not easy there.

Maybe it will help to wiggle it and see if it changes anything:

Otherwise, I can't think of what you can do as a user.

Trying to unscrew the camera and take a look is an adventure. You have to find the screws first.

Otherwise, this is already a photo computer that requires software from Nikon for adjustments of AE and AF, as I read in the SPT Journal.

Andreas Thaler · Feb 4, 2024

The F4 has two common problems:

bleeding LCDs and
resin buildup in the mirror box mechanism. The small apertures are then no longer formed correctly because the aperture lever in the mirror box no longer folds all the way down. The stop down button also makes a buzzing noise when you press it.

Could you check what it looks like on your F4?

I'm trying to solve the problem with the aperture on my F4, but I would have to dismantle the camera to do so. There is a tutorial on this in the forum.

Nikon F4: Quick fix for gummed mechanics parts?

One problem with the Nikon F4 is resin buildup in the mechanics of the mirror box, which prevents the small aperture values from forming. In addition, a scratching noise can be heard when you press the stop down button. The camera has to be heavily dismantled for cleaning and lubrication...

www.photrio.com

Andreas Thaler · Feb 4, 2024

NeillRobinson said:
Hi Andreas - I'll post a picture when I have the camera infront of me, I don't at the moment but give me a couple of hours. I have tried using switch/contact cleaner on all the other switches and buttons, but I could try again? Overall all the contacts look good in the battery compartments but I can check and reclean those if you think it's likely they're causing the issue?

The electronics cleaner probably cannot get to the contacts under the buttons and switches because they are most likely sealed against moisture and dust. A fortress.

Andreas Thaler · Feb 4, 2024

Such cameras either make you happy or unhappy

reddesert · Feb 4, 2024

Check to make sure that the contacts are all physically lined up and that the block holding the body contacts isn't loose in any way - it's probably held in place by a couple of screws. Also, when you have a lens mounted, try wiggling it if there is any play in the lens mount (which there shouldn't be) - especially if you can get it to detect the CPU, try wiggling the lens to see if that un-detects it. It is relatively unlikely that a mechanically loose contact between body and lens (slop) is the problem, but it would explain intermittency and is easy to look for.

NeillRobinson · Feb 4, 2024

Andreas Thaler said:
The contact block may not be screwed completely tight at the top of the mirror box, but you can't get to the screws directly. It could help to remove the bayonet ring. If you can loosen the screws.

But be careful, there are some couplings underneath and the ring for the aperture simulator runs against a spring. Not easy there.

Maybe it will help to wiggle it and see if it changes anything:

View attachment 362056

Otherwise, I can't think of what you can do as a user.

Trying to unscrew the camera and take a look is an adventure. You have to find the screws first.

Otherwise, this is already a photo computer that requires software from Nikon for adjustments of AE and AF, as I read in the SPT Journal.

A lot of points there! Firstly thank you for spending some of your time to think and write your messages about my problem. It is very much appreciated.

And I've had some progress here!

But, firstly - to go over your suggestions

The contact block screwed to the top of the mirror box - it seems tight - I gave it a good wiggle and couldn't detect any movement. I am definitley not unscrewing anything, I would make things worse not better! But it doesn't seem to move even a millimetre, no movement can be detected with the fingertips even when giving it a good wiggle.

Additionally, when wiggling the lens when attached - it is the same - no movement, the thing is absolutely rock solid. Again I could not detect anything, not a milimeter, not even 1/100th of a millimetre, no movement in the lens plate or lens.

I agree about the weather sealing - A fortress, as you've said! I was thinking the same thing, I wondered if it might be possible to spray through the hole in the mirror box where the lens attachment/deattachment thing is - hard to explain but if you look at the lens plate as if it was a clock face, I am talking about the little hole at about the 3 o clock position. I tried spraying some contact cleaner in there and it did seem to go in.

I re cleaned all the lens plate contacts again, and the contacts on the lens itself just to be sure.

I also tried cleaning again every contact I could find with isopropyl and a cotton but. The battery connections, anything at all that looked like a connector in the battery grip. There are little bits of corrosion on the springs in the battery compartment, the bit that your hand holds - but the bit where the battery touches is clean on all, and besides I gave everything a really good clean and a scrub with isopropyl. I don't think it's possible to remove the corrosion more than I already did, I think whats left is just staining / pitting. It's not too terrible anyway.

After trying all this - Still no AF

BUT then I thought about what you had said about that magazine article -
"in the event of AF problems, the AF connector under the base plate can be cleaned. "
Interesting that they mention that, specifically. Perhaps they expect a problem? I tried something a bit risky - holding the camera body upside down, I tried to spray contact cleaner into whatever tiny gap exists anywhere around the contact plate. Above it, below it, through the contacts themselves.. I don't know the architecture of the camera to know what might seep through to where, but I thought hey it's worth a shot. And after leaving the camera for 20 minutes for everything to fully dry - guess what, the AF is now working!

Whether it will *stay* working though.. is another story. I have been here before and I am not (so far) optimistic.. perhaps I should be.

But on the plus side - there *does* seem to be a correlation between that plate, and the issue. If it stops working again I will try nothing else but spraying contact cleaner into/behind the contact plate - if the camera instantly works again then I guess it is confirmed the issue lies there...

Perhaps I just need to carry a can of contact cleaner in my camera bag!

Any thoughts or suggestions, being that spraying the contact cleaner into/on/behind the contact plate *seems* to fix the issue?

Many thanks again for the time spent with me on this so far!

EDIT / UPDATE - Yep, the AF died again. It's definitley SOMETHING to do with that contact block, or the connection behind it. Spraying switch cleaner or using a cotton bud to 'soak' isopropyl alcohol behind it makes the AF work for a while.. then, I guess when it dries out.. it stops working again.

Any ideas, anyone?

NeillRobinson · Feb 4, 2024

Andreas Thaler said:
The F4 has two common problems:

bleeding LCDs and

resin buildup in the mirror box mechanism. The small apertures are then no longer formed correctly because the aperture lever in the mirror box no longer folds all the way down. The stop down button also makes a buzzing noise when you press it.

Could you check what it looks like on your F4?

I'm trying to solve the problem with the aperture on my F4, but I would have to dismantle the camera to do so. There is a tutorial on this in the forum.

Nikon F4: Quick fix for gummed mechanics parts?

One problem with the Nikon F4 is resin buildup in the mechanics of the mirror box, which prevents the small aperture values from forming. In addition, a scratching noise can be heard when you press the stop down button. The camera has to be heavily dismantled for cleaning and lubrication...

www.photrio.com

Hi Andreas -

I am lucky, my example of the F4 exhibits no such issues - all my LCD's are clean, clear and functioning normally - in addition my aperture preview has no issues, and I just checked by taking two terrible self portraits to confirm that at f22 on my 35mm AF-D the aperture does indeed close down all the way to the smallest possible, it seems in that respect everything is functioning nominally.

I did see your post/thread about your issues when I was searching the forums prior to making my post, to see if anyone had already encountered and solved my issue. Reading through it I quickly came to the parts where people were issuing disassembely instructions, and that is way beyond my level!

I wish you all the best in getting yours fixed though, if there's anything I can do let me know.

Andreas Thaler · Feb 4, 2024

NeillRobinson said:
Hi Andreas -

I am lucky, my example of the F4 exhibits no such issues - all my LCD's are clean, clear and functioning normally - in addition my aperture preview has no issues, and I just checked by taking two terrible self portraits to confirm that at f22 on my 35mm AF-D the aperture does indeed close down all the way to the smallest possible, it seems in that respect everything is functioning nominally.

I did see your post/thread about your issues when I was searching the forums prior to making my post, to see if anyone had already encountered and solved my issue. Reading through it I quickly came to the parts where people were issuing disassembely instructions, and that is way beyond my level!

I wish you all the best in getting yours fixed though, if there's anything I can do let me know.

Thanks for the information and your kind offer to support!

Andreas Thaler · Feb 4, 2024

NeillRobinson said:
A lot of points there! Firstly thank you for spending some of your time to think and write your messages about my problem. It is very much appreciated.

And I've had some progress here!

But, firstly - to go over your suggestions

The contact block screwed to the top of the mirror box - it seems tight - I gave it a good wiggle and couldn't detect any movement. I am definitley not unscrewing anything, I would make things worse not better! But it doesn't seem to move even a millimetre, no movement can be detected with the fingertips even when giving it a good wiggle.

Additionally, when wiggling the lens when attached - it is the same - no movement, the thing is absolutely rock solid. Again I could not detect anything, not a milimeter, not even 1/100th of a millimetre, no movement in the lens plate or lens.

I agree about the weather sealing - A fortress, as you've said! I was thinking the same thing, I wondered if it might be possible to spray through the hole in the mirror box where the lens attachment/deattachment thing is - hard to explain but if you look at the lens plate as if it was a clock face, I am talking about the little hole at about the 3 o clock position. I tried spraying some contact cleaner in there and it did seem to go in.

I re cleaned all the lens plate contacts again, and the contacts on the lens itself just to be sure.

I also tried cleaning again every contact I could find with isopropyl and a cotton but. The battery connections, anything at all that looked like a connector in the battery grip. There are little bits of corrosion on the springs in the battery compartment, the bit that your hand holds - but the bit where the battery touches is clean on all, and besides I gave everything a really good clean and a scrub with isopropyl. I don't think it's possible to remove the corrosion more than I already did, I think whats left is just staining / pitting. It's not too terrible anyway.

After trying all this - Still no AF

BUT then I thought about what you had said about that magazine article -
"in the event of AF problems, the AF connector under the base plate can be cleaned. "
Interesting that they mention that, specifically. Perhaps they expect a problem? I tried something a bit risky - holding the camera body upside down, I tried to spray contact cleaner into whatever tiny gap exists anywhere around the contact plate. Above it, below it, through the contacts themselves.. I don't know the architecture of the camera to know what might seep through to where, but I thought hey it's worth a shot. And after leaving the camera for 20 minutes for everything to fully dry - guess what, the AF is now working!

Whether it will *stay* working though.. is another story. I have been here before and I am not (so far) optimistic.. perhaps I should be.

But on the plus side - there *does* seem to be a correlation between that plate, and the issue. If it stops working again I will try nothing else but spraying contact cleaner into/behind the contact plate - if the camera instantly works again then I guess it is confirmed the issue lies there...

Perhaps I just need to carry a can of contact cleaner in my camera bag!

Any thoughts or suggestions, being that spraying the contact cleaner into/on/behind the contact plate *seems* to fix the issue?

Many thanks again for the time spent with me on this so far!

EDIT / UPDATE - Yep, the AF died again. It's definitley SOMETHING to do with that contact block, or the connection behind it. Spraying switch cleaner or using a cotton bud to 'soak' isopropyl alcohol behind it makes the AF work for a while.. then, I guess when it dries out.. it stops working again.

Any ideas, anyone?

I don't think electronics cleaner will do any harm, but it shouldn't be used on parts with lubrication as it will obviously degrease them.

It was a long time ago that I tried to solve my aperture lever problem with this. I sprayed into the opening where the lever moves. At first the problem seemed solved, the lever worked as it should, but then it moved harder than before.

I'm posting the article about the AF Connector here soon, there are also pictures.

Andreas Thaler · Feb 5, 2024

Andreas Thaler said:
I'm posting the article about the AF Connector here soon, there are also pictures.

Here are the referring articles:

The full article is available here. It impressively shows what Nikon's engineers had achieved with the F4:

SPT Journal: January-February 1993

Society of Photo-Technologists Journal

learncamerarepair.com

Andreas Thaler · Feb 5, 2024

Getting to the AF connector should be relatively easy:

Andreas Thaler · Feb 5, 2024

The rubber cover of the base plate should be self-adhesive and removable.

You should use JIS screwdrivers for the screws, but if they are not too tight, a Philips crosshead screwdriver should also do the job.

Whether the cables need to be unsoldered will be determined after the bottom cover has been loosened.

I would try to get to the AF connector like this so that you don't have to spray electronic cleaner at random.

Andreas Thaler · Feb 5, 2024

reddesert said:
Check to make sure that the contacts are all physically lined up and that the block holding the body contacts isn't loose in any way - it's probably held in place by a couple of screws. Also, when you have a lens mounted, try wiggling it if there is any play in the lens mount (which there shouldn't be) - especially if you can get it to detect the CPU, try wiggling the lens to see if that un-detects it. It is relatively unlikely that a mechanically loose contact between body and lens (slop) is the problem, but it would explain intermittency and is easy to look for.

Thanks for your tips!

I'll adopt them for my toolbox

Nikon F4 - Body not 'seeing' / recognising CPU lens - *Sometimes*.. ! Help?

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Nikon F4 - Body not 'seeing' / recognising CPU lens - Sometimes.. ! Help?