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Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 95
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 01, 2010 - 10:59 am: | 
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Just got a used A-1. I checked its meter and it appears to be off by around 2.5 stops. An EOS 1N, in partial metering mode, shows that with ISO speed 100, t=1/1000, f=6.3 is required. The A-1, however, wants f=2.8 for the same scene and settins.
So, the meter is thinking the scene is too dark.
I have the manual for the A-1 and I am reading this. Before I jump in to try to fix this, I wanted some advice from camera repair gurus here.
Any tricks to watch out for while taking the top off?
Any other causes of the meter mis-adjustment other than having to tweak its potentiometers?
Thanks. |
M_currie
Tinkerer
Username: M_currie
Post Number: 219
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 01, 2010 - 01:28 pm: |
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First thing I'd do is make really sure that you're metering the same thing on both cameras, since meter coverage and weighting can differ so much from one to another. Get lenses as close as possible to identical, and aim the cameras at a featureless surface like a wall. If you can find another camera or another meter that you trust, the more the merrier.
If there is really a discrepancy, I'd then make sure that you're using the right batteries, and that their voltage is really what it's supposed to be, because most of the meters I've dealt with overexpose more as voltage drops.
After that, though, I have no experience with the A-1, so that's where I drop out here. |
Gez
Tinkerer
Username: Gez
Post Number: 183
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 01, 2010 - 02:27 pm: |
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There is quite a bit in the archive for the A-1. Important points: the locking collar around the release button must be unscrewed, remove the small metal plate under the slide guard, don't yank too hard on the cover as the small collar holding the red LED may be stuck and you risk pulling the LED away from its circuit board! The good news, there is no fragile spring loaded coupling wire to fight. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 96
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 01, 2010 - 03:05 pm: |
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M_currie: I used an EOS 1N in partial metering mode. I pointed both cameras to the sky. But after your warning, I think I will try a couple of more cameras (EOS 5e and 50e), just to be sure. Meanwhile, I think the exact over exposure is 2 and 2/3 stops (+2.67).
Gez, thanks for the hints. I have been trying to read up on the relevant material here. What really caught my eye was the report of some crystalline substance that builds up on the sensor cell's plastic or glass cover and needs to be scaped off, else it blocks the light reaching the sensor.
https://kyp.hauslendale.com/classics/forum/messages/6900/5420.html
But I haven't been able to find more on this kind of a problem.
Can somebody shed more light on this issue?
Thanks. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 97
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 01, 2010 - 09:22 pm: |
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BTW, that shutter button is a bugger to remove. I suppose that the metal ring around the shutter release button is to be unscrewed (counter-clockwise) and the little switch that is used to select between the Av and Tv is to be left alone?
Pointers about this tricky problem? I have opened a few other cameras, but never got into a situation like before.
Thanks. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 104
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2010 - 02:02 pm: |
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Now, I have the ASA dial off. The A and T slider guard off. The winding level off. The shutter button (the button collar with the button, the A and T selector switch and a washer underneath it) off.
The screws from the top cover are off too (after I removed the bezel(?) from around the lens mount).
The viewfinder display switch is "on".
Now, is that it? Should I take the cover off? It is a bit stiff. I tried to slide it upwards, but it seems to be stuck or something. Have I missed something? |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 106
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2010 - 02:54 pm: |
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Okay, I was missing to take off the little screw in the viewfinder blind. It is in the blind switch (left of viewfinder) covered by a little plastic dot like cover. Took off the cover, removed the screw under it and removed the blinds switch.
The top is more loose now.
However, I think it is still sticking at the red LED or near it some place. Suggestions? |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 107
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2010 - 03:07 pm: |
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Well, so here is what I did. Dropped couple of drop of naphtha on the LED. Left for some minutes. Then, while holding the LED down in place using the back of a plastic grip of a screw driver, I gently nudged the cover upwards away from the body while giving tiny rocks to it. When I noticed that the LED did not appear stuck to the cover anymore, I was able to lift off the cover easily.
Thanks to Gez who pointed out this factor in a post above. |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 108
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2010 - 03:53 pm: |
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So far so good. The top is off. Desoldered the black wire and now the top is separate from the body.
Is that only wire that connects the body to the top?
Next, I need to do two main things:
1. Clear the view finder lens' inside.
2. See what is the cause of meter being off by a constant margin.
How do I take out the view finder? |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 109
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 02, 2010 - 08:40 pm: |
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Well, got the eye piece out. Just had to remove the two screws on its two sides, from top. With those screws out, the frame around the eye piece becomes unsecured. That frame has a flex circuit connected to it from the right, and two wires, an orange and a white at two places on its left. In the middle of that frame, near the top of the prism, sits the photo cell.
I was able to clean the inner side of the eye piece and also the side of the prism facing the eye piece. So that is done.
Finally, I also checked the photo cell's side facing the prism. It appeared to be clear and clean. The pattern inside the cell was clearly visible. No fog on the photo cell's surface.
How does this related with the constant difference of +2.67 stops in the exposure measurement by the camera? Basically, the camera sees the seen as 2.67 stops darker than it actually is. The battery is good, even tried with a different new battery. Suggestions what could be wrong with the meter? |
Nico
Tinkerer
Username: Nico
Post Number: 1
Registered: 07-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 17, 2010 - 12:32 pm: |
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Hi Phototaker! I have the very same problem! I've made the same comparation with a Minolta Hi-matic 7s and a Canon Ae-1 and concluded that the difference between meters is also about +2 and 2/3 stops. Until now, I've been using the camera anyway but with an adjustment of the ASA setting (If i wanna shot a 100 ASA, set the dial at 800), but now I want to shot on very dim light situations using pushed film at 3200. That is imposible with the meter as is since the dial goes to 12800 max (which is very generous, I don't complain).
So I wanted to ask you if you finally solved that problem and if you could post your conclussion here. I know i'm a little lazy but wanna know before taking the cover up and screw it all.
Hope you'd fixed it
Regards |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 213
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 25, 2010 - 08:48 am: |
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I have replied to the private message you sent me (don't worry about having to send me a private message, I don't mind it). But please continue this thread here. You have more chances of help here.
I haven't fixed the issue yet. I compensate for it by using the ISO setting, as you did. I must admit, I haven't used the camera all that often in the past some months, only a few rolls. Been quite busy with life and couldn't get time to tweak my camera as much as I wanted to, or to frequent and post on this forum.
However, I have since looked at the repair manual for the A-1 and I have identified the variable resistors on the camera that can be changed. If you like, I can post photos showing them and describing which one changes the meter setting for which level of illumination.
The main reason I haven't changed those resistors in my camera is that I wasn't sure if the resistors' settings needed changing, or whether the sensor (the photo cell) was dirty or fogged or whether the ISO setting dial itself was misaligned. Of the two latter reasons, I have verified that the sensor is clean. I have tried to verify the ISO dial setting and it appears to be good. The only thing left to verify these two settings is to actually check their output with an oscilloscope, a step that I haven't done yet. If I had done the test with a scope, I would be quite confident in saying that the variable resistors need changing to adjust the meter sensitivity. I suppose a person can try the resistor directly as a first step to compensate for the error.
If you like, I can dig out and post photos that I took while I had the camera open. They show clearly which resistors I am talking about.
If you don't have the repair manual for the camera, or can't find it on via google, let me know and I will send it to you via email.
Good luck! |
Nico
Tinkerer
Username: Nico
Post Number: 4
Registered: 07-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 25, 2010 - 10:13 am: |
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Ok! thank you for you're almost immediate response!
Thats right, we made the same thing to compensate for the very same problem, but you know it is very annoying too... I would like to shoot at 12800 ASA someday!! (It will be probably not grain but stones of silver on the pics but who knows!)
I do, actually, have the repair manual for this camera and it is a very lame desing if you ask me, but i think their were all the same back then. Maybe I'm just not used to those kind of literature, since i'm not really a technician. I work repairing DVD´s and digital camcoders but don't like (nor know) much about electronics, what an irony...
But I love repairing and restoring classic cameras!! And certainly love making things work on my own without paying someone else.
Thats why I look for help before messing around with it. I'm sure I can manage this thing anyway.
If you want i can send you what I have as a service manual to see if you have the same thing.
It would be really nice of you if you post those pics so I can see exactly what resistor you're talking about. I Don't want to turn the self destruct one.
In the case it were the resistor, what I wonder is why our two cameras have EXACTLY THE SAME misalignment of +2 2/3 stops.
It'd make more sense if they were different. Since it would be an electronic problem, it would probably be a more random shift.
Seems that they had the same cause, and I bet there is someone else who had to suffer this too.
I hoped it were caused by a shift of the film speed dial or something like it, as you say, cause I've read its a common thing. I think I'm gonna check it anyway.
Thank you again for you're very cordial reply, feels like there are men (and women) of good will here.
Good luck for you too.
(I am soooooooooooooooo slow writing in english, it is so exhausting, haha!) |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 215
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 25, 2010 - 12:57 pm: |
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I wasn't able to see how the film speed dial could have shifted. If you know any references that show this, it would be great to know. I haven't tweaked the resistors only because of this reason.
I have attached the photo of the variable resistors that are accessible once you remove the top of the camera. The resistor are atop the prism toward the front of its right side. The top edge of the viewfinder is visible on the lower left of the photo.
The instructions for adjustments are given on pages 108 and 109 of the PDF file (not the page numbers that appear in the document) of the service manual. If you don't have the same one, let me know and I will send it to you via email.
Regards.
 |
Nico
Tinkerer
Username: Nico
Post Number: 6
Registered: 07-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 25, 2010 - 09:02 pm: |
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Well, tanks you a lot. I think this week I'll have some time to spend on it. I'll let you know as soon as I can.
Oh, seems that I have the same manual as you.
But let me ask you what do you understand about the "ASA Brush Adjustment" that is detailed on page 110 of the PDF. It says it adjusts the something about exposure but I don't understand quite well how to. Says you need a "SV Check Bit Tool"... ¿? could be it a binary code reader or something...?
Bye! |
Aphototaker
Tinkerer
Username: Aphototaker
Post Number: 216
Registered: 12-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 25, 2010 - 10:44 pm: |
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I am not sure either about the ASA brush ring. I will need to read the manual again to hazard a guess.
The SV check bit tool probably is a digital display that shows the binary code (or octal) for the bit patterns it sees. I suppose one can do the same thing with an oscilloscope, only that in the scope the bits have to be read manually from the detected waveform. The basic thing to care about, while reading the signals, is to use the proper trigger (it is available on a contact on the flex PCB, right above the prism, for convenience).
On a related note, you may get more details of these terms from the manuals for AE-1 and AE-1 Program cameras. Some of the documents available on the web for these cameras explain what these signals mean. The manual for the A-1, on the other hand, is quite terse. It appears to be written for a person already quite comfortable with the terminology. Some manuals for the other two cameras are written in an introductory fashion, however. So they are a good help. |
Davsmiths
Tinkerer
Username: Davsmiths
Post Number: 1
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 09, 2011 - 11:42 am: |
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Hi,
I'm getting the exact same problem with my A-1. The metering is positive 2+ EVs.
How do I solve this issue? |
Davsmiths
Tinkerer
Username: Davsmiths
Post Number: 2
Registered: 04-2011
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 09, 2011 - 11:48 am: |
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Hi,
I'm getting the exact same problem with my A-1. The metering is positive 2+ EVs.
How do I solve this issue? |
Verduzcor
Tinkerer
Username: Verduzcor
Post Number: 11
Registered: 10-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 21, 2011 - 10:43 am: |
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Hi everybody, I sow some troubles with this camera alike yours, I would check if when taking upper plate off don't damaged anything (SW3), here the words of Guru Glenn (God save you Glenn) "It is most important that you set the viewfinder info switch, under battery test button to the on position - towards white dot. If this is not done, you will make a bloody mess of the switch contacts!", another possibility is the blue layer covering the cell, make a search about this, I can't find the post. |
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