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Wildestseas
Tinkerer
Username: Wildestseas
Post Number: 3
Registered: 07-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 12, 2009 - 06:18 pm: | 
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Recently while on an outing with my Olympus XA I noticed that the shutter speeds suddenly seemed to be a bit long for what the needle was indicating. When it indicates 1/500th of a second, the shutter speed sounds like it was around 1/30th. I just got back a roll of slide film today that confirms this. Exposures that were in the range of 1/10th to 10 seconds were beautiful. Anything shorter than that, however, is overexposed.
I first replaced the batteries but this did not help. I have read on some forums that other people attribute this type of problem to dirty magnets in the shutter assembly.
Since the camera was $40, and repair would probably be around $100 I decided to attempt a repair myself. I've nearly disassembled the camera, however, I'm pausing before delving into the lens/shutter assembly.
Before I take this apart any further, do any of you have any advice as to where you think the problem lies? Do you think I'm on the right track?
Thanks for your thoughts! |
Olympfix
Tinkerer
Username: Olympfix
Post Number: 14
Registered: 05-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 14, 2009 - 12:48 am: |
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When the back on an XA is opened, a switch is made (turned on) to set the shutter at 1/30 or so to allow the film to be advanced and shot when loading with the front cover closed. It's connected to the counter reset , -check to see it's going off when you simulate the back closure. |
Wildestseas
Tinkerer
Username: Wildestseas
Post Number: 5
Registered: 07-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 15, 2009 - 02:12 pm: |
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So over the course of several days I nearly completely disassembled the XA and gave it the cleaning of its life. The shutter blades definitely aren't sticky. Upon re-assembly (which I believe to be a heroic feat in itself) the problem with the overexposure still persists. I discovered something very interesting, however:
As I said previously, the camera meters perfectly at speeds lower than about 1/10th of a second exposure times. (This is why I initially ruled-out the light meter as the source of the problem.) In brighter light when the light meter needle reads about 1/500th, the shutter speed sounds like it's somewhere around 1/30th of a second.
If I take a powerful flashlight and shine it directly into the sensor at f/2.8 and ISO 800, I can get the shutter to sound like it's going off at around 1/500th of a second (even though the appropriate exposure would probably be much shorter). This shows that the shutter is, in fact, capable of firing at all the speeds for which it was designed.
This is baffling - I'm not an expert on the operations of light meters, but it seems odd that one could take adequate readings at low light levels but become less sensitive in bright light. Also the fact that the light meter shows appropriate readings in regards to the shutter speed indicator makes me wonder if the fault lies neither in the light meter nor the shutter, but in some mechanism in-between.
I examined the switch that Olympfix mentioned above, but believe it to be functioning properly due to the fact that when engaged it should limit the exposure to 1/30th of a second regardless of the light meter reading.
If I can get this XA operational again, I think I'll quit my day job to repair these things full time. |
Chenard
Tinkerer
Username: Chenard
Post Number: 30
Registered: 11-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 27, 2009 - 10:04 am: |
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The XA has different circuits for the display in the viewfinder, and actually controlling the shutter. There are a couple of pots/wipers on the ceramic circuit board on the front of the camera. One of them determines where the battery check light kicks in, and the other one controls the exposure. At the moment I forget which is which, but some quick experimentation will quickly tell you which is which.
My XA used to do exactly what you describe. The problem was that the CDS cell for the meter ciruit had aged and was no longer capable of becoming very low in resistance in bright light.
A difference of a few hundred ohms in bright light will cause poor exposures in bright conditions, but not so much in low light conditions because CDS cells are logarithmic in nature--the hundred ohm error doesn't matter so much on a base resistance of say, 25Kohm, so the low light exposures are still quite close.
In the case my my XA, replacing the meter cells and recalibrating the meter restored the camera to correct operation.
I suggest you check the wires to the cells, and make sure that there is no resistance being "added". Then try adjusting the wiper to see if you can arrive at an acceptable calibration over the range of light levels that you will be shooting. Let us know....
Paul |
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