Nikon F3 dead, but happy with MD4 half press!!

I’ve been helped a lot in past few days by Andreas Thaler,,, so big thank you to him and hope to continue to pick his brains ;-))

I'll try to describe issue as best I can.

F3, dead, no display or shutter. Good battery but no power, nothing. Mechanicals all fine (although camera is missing the memory button on the manual shutter release).

Add MD4, fires perfectly from the drive shutter button, meter and LCD great in camera good. While the LCD is displaying data (half press from MD4) the camera shutter button works as well as the MD4 one. If I wait till the LCD goes out,,, (the 16 second timer) half press on camera shutter does nothing and does not fire,,, half press on MD4 again works and shutter fires from drive AND camera.
So, camera works fine ONLY while the LCD 16 second period is active from a half press on the MD4. That is camera AND drive shutter release. All speeds seem to be fine and meter working.

Using the CC Nikon F3 trouble shooting guide I have used flow chart 1:A and got as far as:
OK > OK > No > Yes! which gets me to:

"Check release button power
switch and continuity from
TP-3 to the power switch"

I only have the base of the camera off so far. So at this stage I clearly need to look at what happens between TP3 and the shutter button.
The confusing thing is why would the CAMERA shutter button be working fine only when the LCD is active (that 16 sec period) after an MD4 half press??

Anyone come across this before?
Would be useful to know a bit more if possible before starting the disassembly.
I’m going to post this on Photo.net also as there might be users on there who are not on here.
Hope the above makes sense. I read a ton of stuff on various forums but don't post often. I'll try to.

BIG Thanks to Andreas for his help and his words of wisdom so far. Much appreciated.

Bigpatty said:

I only have the base of the camera off so far. So at this stage I clearly need to look at what happens between TP3 and the shutter button.
The confusing thing is why would the CAMERA shutter button be working fine only when the LCD is active (that 16 sec period) after an MD4 half press??

Click to expand...

I don't know the answer to what is wrong for sure, but there is a logical answer to this question, which may help guide where to look. The shutter release on cameras with a half-press is often actually two switches (electrical or mechanical). In the case of the F3 the first switch on half-press powers the camera on, and the second switch fires the shutter. In your camera the first switch in the body isn't working, so the camera doesn't power on. But if you power it on by half-pressing the MD-4, then the second switch in the body can close its contact and fire the shutter.

It might seem like pressing the body release all the way should provide power to the camera and allow it to fire, but for whatever reason the F3 isn't wired that way.

Here is a screenshot from the repair manual showing mechanically how the two switches work. (Ignore the "troubleshooting" paragraph as that's related to a different item on the same page.) It is possible that the problem is not in the mechanics, but somewhere in the electrical contacts: for example if part 11 is disconnected from the power circuit, but part 12 is still connected to the release electromagnet, then it's possible that pressing the button all the way would not power up the camera, but would still fire the camera if powered up from the MD-4.

reddesert said:

I don't know the answer to what is wrong for sure, but there is a logical answer to this question, which may help guide where to look. The shutter release on cameras with a half-press is often actually two switches (electrical or mechanical). In the case of the F3 the first switch on half-press powers the camera on, and the second switch fires the shutter. In your camera the first switch in the body isn't working, so the camera doesn't power on. But if you power it on by half-pressing the MD-4, then the second switch in the body can close its contact and fire the shutter.

It might seem like pressing the body release all the way should provide power to the camera and allow it to fire, but for whatever reason the F3 isn't wired that way.

Here is a screenshot from the repair manual showing mechanically how the two switches work. (Ignore the "troubleshooting" paragraph as that's related to a different item on the same page.) It is possible that the problem is not in the mechanics, but somewhere in the electrical contacts: for example if part 11 is disconnected from the power circuit, but part 12 is still connected to the release electromagnet, then it's possible that pressing the button all the way would not power up the camera, but would still fire the camera if powered up from the MD-4.

Click to expand...

Thank you for the insight. It seems logical and I had thought that the half press was the reason for all the issues (my notes on photo.net, same posting). You have given me all I need now to probably go straight to the issue.
Brilliant.
Will take me a little while to get to that switch, but I will report back on what happens.
I'll also share your insight on the photo.net thread.
Very exciting, fingers crossed it's easy to repair.

Getting there. Work stopped for today,,,

Update. Fixed ;-)
I suspect that the power issue was just dirt on the half press contacts and/or the power sw under the advance lever. I removed the advance lever assembly and the speed dial as per the guides and cleaned the contacts. I also cleaned the power switch contacts. Not easy because they are so small. I used some stiff paper soaked in contact cleaner, holding the contacts closed and moving the paper back and forth. After this using a small probe to push the half press contact down the lcd came alive,,, full press and the shutter fired (I had it set to bulb when I removed the shutter speed dial so that was all I could test at the time).
Due to it being such a quick clean and it looking good I had a general clean up, little lube in one or two spots and reassembled to test further. I didn't take any photos because there was nothing out of the ordinary to see.
Once in a state where it could be advanced and then fired over and over and I could adjust the speeds.

All the speeds from "T", "B",, and slow speeds up to "60" fired fine, seem correct and they all displayed correctly in the lcd display.
Then instead of "125" it showed "80" in the display and remained at 80 all the way up to "2000" and "A".
The last time I owned an F3 (an HP) was in the early 90's. So bare with me.
I'd had the back off (as you need it off or open to get the advance mech. plate back easily where the counter reset pin is). By the way, for anyone doing this for first time I always place a piece of an old business card or an old cut plastic card over the shutter and tape it there while working with the back open or off, trust me,,, your finger will ruin the shutter if you don't do this!!! ;-(.
Then I remembered the F3 defaults to 1/80 until frame 1 for some reason (remembered after a cup tea and readying the manual). So I replaced the back, advance to frame one and bingo,,, all other speeds good. Even the illumination in the LCD works ;-)

I have a working F3 !!!! Very happy.
I might now removed the left side and just give the ASA dial and flash shoe area a good clean as the ASA dial is very stiff and might have dirt it it.
Just need to source an exposure memory button now (in the mech, shutter release) and maybe a better focusing screen as someone has marked it.

So probably just a bit of light oxidisation or debris on the electrical contacts.
And as per the CC flow chart,,, the issue was continuity from TP3 in the base to the two power switches (main and half press).
Hope this helps anyone with same issue.

Cheers all and thank you..

Bigpatty said:

Cheers all and thank you..

Click to expand...

Thanks for keeping us updated!

Welcome to Photrio!

Bigpatty said:

I used some stiff paper soaked in contact cleaner

Click to expand...

I sometimes use fine grit sandpaper for this kind of thing. Don't tell anyone - and don't overdo the back & forth; just a couple of passes and check whether functionality is restored. Much of the grime you get in a place like that tends to be pretty stubborn. In a camera like this, the contacts will be gold-plated, so at least no oxidation of the contacts proper.

Anyway, easy enough for me to say after someone's already fixed it! Well done, and thanks for sharing the solution with us!