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Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 108
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 04:01 pm: | 
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I haven't owned this camera long -- less than a month. The meter has worked reliably since I bought it. I set it on the shelf a few days ago, then went to use it a short while ago, and the meter was unresponsive.
Well, I figured the battery adapter I had cobbled together for this finder had gotten out of alignment and checked it out, confirmed that it was positioned correctly, and it didn't make any difference. I changed out the battery, even though the existing one was still reading correct voltage. No change.
I inspected the contacts for corrosion. No recent corrosion, although there are some slight traces of earlier corrosion.
I use 675 hearing aid batteries for my cameras that require the old 625 mercury ones and they are smaller than the originals, hence the adapter. But the way this finder's battery compartment is configured, I can take a small battery and push it up against the side of the compartment, which is where it picks up the + side of the voltage, while still having it touch the center contact, which is for the - connection. Doing this, there was still no response from the meter.
Oh crap.
So I whip out my multimeter and check to see if maybe something's come loose inside. I set the ohm range to 200 and I get "open," then I set it to "2000" and I get "open," then to "20k" and still "open." Finally I set it to "200k" and I get a reading. It bounces around a lot, but it reads around 160k ohms. Now, this seems to be very high to me, but what do I know?
And then, as I'm sitting here typing, it occurs to me to see if it makes any difference with the resistance values if I change shutter speeds and/or apertures. So I do this, but now I'm getting open readings again, all the way up to 2 mega ohms. So, pretty satisfied that there's no low-grade short anymore, I try the battery + adapter again, and whatdayaknow. It works.
Even though I did all the shutter speed and aperture ring changing before all this, suddenly it seems to work again.
So I'm figuring that if it's happened once, it'll happen again and next time it does I'd like to know what I need to do to fix it permanently. Any ideas what might be causing this? And do you think that 160k ohm reading I was getting was indicative of the problem?
As always, TIA. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 109
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 04:32 pm: |
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Just thought I should check back in. The meter being back to working normally didn't last very long. Like a few minutes. I was about to take the camera out and burn through some film but the meter was unresponsive again. Pulled out my multimeter to measure resistance across the battery contacts, and sure enough, I'm getting a resistance reading that bounces around a lot, but that is now closer to 150k ohms. Sort of.
Also, I have a question that I forgot to ask earlier. The old Nikon F's electrics use a positive ground, don't they? Don't see that too often outside of old British motorcycles, I've found. |
Michael_linn
Tinkerer
Username: Michael_linn
Post Number: 11
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 05:23 pm: |
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I don't know if this will be any help, because I'm trying to recall a distant memory, but if I recall correctly, some of the early photomic finders had a problem with the substrate of the aperture value resistor cracking, causing an intermittent or permanent open circuit. Just a guess! |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 110
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 05:57 pm: |
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Thanks for checking in, Michael. I dunno if it's the same circuit or not, but with what I'm dealing with right now, the meter is working with an open circuit between the two battery contacts and stops working when it shows a slight resistance -- about 160k ohms -- between the two contacts.
Part of the problem with these early Nikon finders is too often one is calling upon distant memories . . .  |
Brcamera
Tinkerer
Username: Brcamera
Post Number: 100
Registered: 08-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 06:18 pm: |
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All of the Nikon meter heads, from the non-TTL original Photomic through the F2 share a common part and that is a resistor band with "fingers" making a sliding contact on the band. This is the first spot to check as the contacts get dirty and cause all kinds of intermittent issues, normally a jumpy needle. On your original Photomic finder, it is fairly easy to inspect the contacts, just remove the four screws on the bottom of the finder and the prism assembly will remove from the head. You can see the golden contacts and the resistor band at this point... |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 111
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 11:22 pm: |
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Thanks for the tips, Br. I removed the prism assembly and noticed something interesting. The brass gear that has the meter rings in it turned one way but not the other, and then once it had turned all the way in one direction, it wouldn't turn at all in either direction. So I ended up dismantling the shutter speed knob assembly, which showed what was wrong. When I first bought this camera, the top ASA dial and even the knurled ring were loose. Found out that the central screw held them down, which I tightened with finger pressure. Well, I dunno if finger pressure would have been enough to hold everything in place or not, but I think the dial being out of whack had already occurred. So it took some finagling to get the dial's pin into this brass fork concentric with the shutter speed dial's shaft, and then I had to get the shaft lined up with the shutter speed ring. Well, anyway, I got all this done, and snugged it down with the top screw. I peeled the bit of leatherette off the top of the top screw, though, which revealed a couple of holes, so I was able to use my tool for these sorts of screws and caps and snugged it down good. Now the brass gear turns both ways.
Oh, and while I had it apart, I went ahead and swabbed down the wipers and the ring with alcohol. I have a tiny miniature swab I use for this. So the swab picked up some gray stuff. Not much.
The wipers for the shutter speed have made some pretty significant marks on the resistor, whereas the wipers for the aperture ring have made very few marks at all. The shutter speed wipers are two fairly prominent pieces whereas the aperture wipers are about four or five much thinner brushes, which is why I think they haven't made much of a mark on the ring. Frankly the level of wear on the shutter speed side has me somewhat concerned.
Well anyway, so I get everything back together, and the meter works. Yay! So I mount the finder to the camera and check it again, and it's gone out again. Pulled out my multimeter and this time I'm getting open readings between the battery contacts at all resistance settings. So, so much for that.
So I have an intermittent condition. When the meter works, it's accurate. And it's been working consistently until today. Dang it. When I had the prism out I took a look at the wires and didn't find any obvious loose connections. Probably should give things a closer look I guess. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 112
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 16, 2011 - 11:53 pm: |
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Crap! I think I need to say "never mind." I think I need to redo my adapter -- or buy one of those that a guy sells over the net, but whose web page I don't have handy. I've been able to get the meter to respond by wiggling the adapted battery at one exact spot. So I think all this is due to my funky adapter. Glad I fixed the problem with the resister gear ring though. |
M_currie
Tinkerer
Username: M_currie
Post Number: 264
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 21, 2011 - 07:07 am: |
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If you have doubts about the battery adapter, you might try, just for testing purposes, an alkaline battery of the correct size. I think they're still available, possibly still at Radio Shack. They still exist, at least for a while, on the internet, from Batteriesinaflash, and others, although the silver oxides are just about nonexistent. The alkaline will give you high meter readings and may be too far off to compensate with the ASA dial, but it won't hurt the meter, and if the meter works consistently you'll know not to worry about the innards.
If you've had the meter open, you might also consider recalibrating it for the higher voltage. I don't know how, or whether, the old Photomic can be done easily, but the later FTn meter is pretty easy to readjust, and all mine now run on silver-oxides or alkalines with reasonable accuracy. |
Cooltouch
Tinkerer
Username: Cooltouch
Post Number: 113
Registered: 01-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 21, 2011 - 11:05 pm: |
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Thanks for checking in, M_currie. Actually all my adapter is is a piece of solid-core ~14 ga. household wiring wrapped around the 675 battery. This works well enough so's the battery's + side makes contact with the sidewall of the battery compartment. Yeah, I've thought about buying a 1.5 volt 625 replacement just to see if it works, but I'm quite confident that I'd just be wasting my money.
In my very first post in this thread, I mentioned that I can make contact to both the center (-) contact and the outer wall (+) just by holding the smaller battery in the right position so it touches both. When I do this now, I'm getting no response. And I think that when I was getting a response by just holding the battery at one exact spot, as I mentioned in my immediately previous post, that this happened to coincide when the meter felt like working.
Right now, I suspect that there is something open somewhere -- a loose connection, loose solder joint, broken wire . . . probably something simple like that. I just don't see the meter cycling from working normally to being totally dead as being a symptom of some complex inner set of electronics going buggy. Heh. What electronics? And even though the shutter speed side of the meter resistor shows a fair amount of wear, I'd expect to see a jumpy meter rather than it just quitting altogether some times and working at other times.
Next step is to open up the finder again and work my way into the area immediately behind the battery chamber. Look for something loose. Go for the easy stuff first.
Actually I've been putting things off . . . dunno why.
I've also looked high and low for a scan or .pdf of a repair manual for this old finder, but haven't come up with anything yet. I don't suppose anybody here would have a copy? |
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