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Flor27
Tinkerer
Username: Flor27
Post Number: 1
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 23, 2008 - 09:06 am: | 
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Hi all,
I'm looking for hints to adjust the meter of my Minolta X-500 (european version of X-570) and SRT-100x scamera. It shows signs of heavy under/over exposure with fresh battery.
Any hint, links to service manuals, trim pots locations are welcome 
Cheers |
Mndean
Tinkerer
Username: Mndean
Post Number: 70
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, August 24, 2008 - 11:14 pm: |
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The SRT-100x uses a 625 mercury battery, which is not made anymore. The replacement 625 alkaline battery won't work well, since its voltage starts too high and drops over time. There are many different ways of getting around this issue, but none are foolproof. You can use a Wein cell, adapt a 675 zinc-air cell, or use an S76 silver cell with a diode to drop the voltage. None of these workarounds are perfect. I use the 675 cell and adjust the ASA rating, which seems to work reasonably well for me.
Your X-500 shouldn't have such a problem, but someone here might have an idea what's causing the trouble. You don't specify the problem with your X-500. As you say, it may need adjustment. |
Flor27
Tinkerer
Username: Flor27
Post Number: 2
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, August 25, 2008 - 04:14 am: |
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I'm using still 1,35v mercury cell in the SRT-100X actually. After some tests against my EOS 5D, this camera's exposure system is perfectly adjusted.
But the X-500 still overexpose about 1 1/2 step and I need to adjust it. |
Don
Tinkerer
Username: Don
Post Number: 40
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 28, 2008 - 11:57 am: |
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Are you using the same lens to check metering on both bodies or are they 2 different lenses? If different, check the meter coupling pin on the rear of the lens to see if its bent & if so, carefully straighten it. Not sure if this model has exp. comp but if so check that also. If not, then the pots under the top need adj. Might be easier to compenste by adj the asa dial |
Juan_b
Tinkerer
Username: Juan_b
Post Number: 3
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 29, 2008 - 02:36 am: |
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I have the same problem with a SRT-303. |
Markus
Tinkerer
Username: Markus
Post Number: 74
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 29, 2008 - 08:45 am: |
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Juan_b:
The SRT's have two light sensors that are cemented to the penta-prism. These can come loose and as a result you'd see erratic exposure values with the meter. I would take the top off the camera and take a look. If you are using a zinc air battery you should see correct exposure values, or at least you should be able to adjust the meter.
BTW, after checking in Tomosy's book, to get the mechanical adjustment right, you need to set the ASA dial to 100, and put on a lens that is set to f/8. In that configuration, when you turn the shutter speed dial from B to 1000, the reference circle should move all the through its entire range without overlapping with the end marks. If it doesn't, adjust it mechanically using the brass eccentric screw on top of the meter unit. Then, to fine tune the meter, stick a styrofoam cup over the lens, and point the camera at the sun around noon. This is equivalent to incident light metering at sunny 16 (I read somewhere that one should use a 50mm f/1.7 lens for that, but I don't quite understand why). Make sure that the camera's meter reads accordingly (f/16 at ISO 100 and 1/125 sec), if not, adjust the variable resistor under the bottom plate. There should be enough leeway to adjust this resistor to silver oxide batteries, however, it is quite easy to upgrade the circuit with a Shottky diode such that a silver oxide battery yields the same voltage as a mercury cell w/o the diode (this is what I did, since without the diode the variable resistor had to be turned almost all the way to on end of its scale).
I've adjusted my SRT Super in that way and I manage to get good exposures with slide film in it just using the built in meter. |
Don
Tinkerer
Username: Don
Post Number: 41
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 29, 2008 - 11:50 am: |
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On the X 500,(or most MC/MD mt Minolta) check the freedom of movement of the diafram metering ring just behind the lens mt. It's tab should sit between the red dot & the L top screw on the lens mtg. ring. Push it ccw all the way -- it should return quickly to the starting position. Sometimes, dirt can slow the movement which in turn affects the meter readouts. If the action is sluggish, a drop of lighter fluid should free it up. |
Mndean
Tinkerer
Username: Mndean
Post Number: 73
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 29, 2008 - 09:51 pm: |
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Ah, I just remembered something I read on an X-700 site dealing with the X-series cameras. There's a variable resistor ring that transmits aperture information to the camera. If it's broken, or one of the wires is broken, it can cause the problem you see on your X-500. I'd take that as a worst-case scenario. Cleaning the ring would be the first step, then if the problem doesn't go away, consider it might be a more serious problem.
Okay, I found the page (had it bookmarked)
http://twid.de/x700/disas.html
The ring is shown in the second row of pictures, in the last column. I hope it's not that serious a problem, but even if it is, there's a lot of dead X-series cameras to get parts from. |
Mndean
Tinkerer
Username: Mndean
Post Number: 74
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 29, 2008 - 10:00 pm: |
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Markus,
You've had good success with Tomosy's approach? I just used a 675 zinc-air battery and adjusted the ASA which works fine, but adjusting the pot is more elegant. I still wouldn't change from the 675s (I have a couple dozen of them), but I would happily adjust the pot. Much thanks for the project idea. |
Markus
Tinkerer
Username: Markus
Post Number: 75
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 29, 2008 - 11:52 pm: |
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I did have to adjust the variable resistor. I was quoting Tomosy just to make the point that to get the correct EV range for the meter, the mechanical adjustment must be correct. After that you must adjust the resistor to get correct meter readings. Adding the Shottky diode to the circuit is trivial, see
http://flickr.com/photos/74695037@N00/1359149803/in/photostream/
for instructions for the Konica Auto S2 (but the SRT is similar). |
Juan_b
Tinkerer
Username: Juan_b
Post Number: 4
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 30, 2008 - 08:32 am: |
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Markus: I've taken off the top of the camera and the sensor are fixed hardly. In the bottom of the camera, there are two resistors. One of these is for adjust the battery checker and the other is for adjust the light meter, but this one only can adjust very few the light meter and I need to adjust more.
I don't like it, but I've had to adjust the position of the arm (with the ring) that it appears into the viewer.
Now, I've checked the camera lightmeter reads and they are good in all the light conditions.
I have not been able to adjust the lightmeter trought the resistors. |
Markus
Tinkerer
Username: Markus
Post Number: 76
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 30, 2008 - 11:43 am: |
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Juan, what kind of battery are you using? If it is a silver oxide battery then the resistor will probably not provide enough play to adjust the meter and you will have to also mechanically adjust the reference circle, as you did. If you do that, however, your meter will have a smaller light value range, which is probably not a big deal. If you've got it to read correctly, for most condititions, that should be good enough. |
Juan_b
Tinkerer
Username: Juan_b
Post Number: 5
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 30, 2008 - 02:01 pm: |
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Markus, I've tried a 1.35V Wein cell and an alkaline 1,55V, but ever the arrow of the light meter is too up in the screen. I can adjust the battery cheker trought the resistor but I can't do the same withe the light meter with the other resistor. I don't know what is happening. |
Mndean
Tinkerer
Username: Mndean
Post Number: 75
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 30, 2008 - 07:29 pm: |
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Markus,
I checked the mechanical adjustment again (I did it when I bought my 102 some time ago after reading something about checking it...somewhere), and it's still exactly within the limits, so the styrofoam cup into the sun adjustment is all that's left. I may do as you suggest and put an inline Schottky diode and adjust the variable resistor, it would make all my Minoltas use S76 cells which would simplify matters since they're the cameras that get the most use for me. I just picked up a nicely working X-700 for $20, with late MD 50/1.7, and power winder G. Serial number is below the range with the dodgy electrolytic caps (it's in the 21xxxxx range). Only problem is a small crack in the top deck that I'm going to epoxy over and maybe later replace it when I can find a clean parts X-700. |
Markus
Tinkerer
Username: Markus
Post Number: 77
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, August 31, 2008 - 02:46 pm: |
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Juan, I was looking at Tomosy again, and he notes that persistent problems with properly adjusting the meter on an SRT might be caused by yellowing optical cement that keeps the CdS cells on the penta prism. They are glued with Canada balsam and he recommends cleaning the Canada balsam off with acetone and re-cementing them. Since this is not in the optical path of the camera (only for measuring light), he says that regular clear glue should work fine if you don't have Canada balsam or some optical cement. |
Juan_b
Tinkerer
Username: Juan_b
Post Number: 6
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 01, 2008 - 07:37 am: |
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Markus, I think that you're right. When I took off the cover, I saw that there are some orange Canada balsam arround the cells. Then it's very likely that the balsam is between the cells and the prism.
When I have some time, I'll take off the top plate, I'll clean the balsam and re-glue the cells.
Thanks a lot! |
Markus
Tinkerer
Username: Markus
Post Number: 78
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 01, 2008 - 10:30 am: |
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Just a word of caution, I'm sure you are aware of this, but acetone can do a lot of damage to plastic... so you should be extremely cautious with it. |
Flor27
Tinkerer
Username: Flor27
Post Number: 3
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 19, 2008 - 09:36 am: |
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Thank you all people for the numerous tips about those Minolta cameras !
I will try to check the X-500's aperture resistor state behinf the mount first.
Thanks again ! |
