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Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 10, 2005 - 06:26 am: | 
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The lightmeter of my Topcon Uni seems to be one step off at EV 8 or so and below. I found a small board with a variable resistor under the prism housing. Does anyone have experience or even a circuit diagram to show how to adjust this? I could possibly figure it out myself but help will be appreciated. |
Lars
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 11, 2005 - 02:33 pm: |
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Winfred,
First of all; make sure you use the right batteries. These cameras where designed to run on 1.35V Mercury cells. Camera batteries today are either 1.5V Alkaline or 1.55V Silver oxide, which may cause the problem You describe. The best solution is to use Zinc/air batteries rated at 1.4V, which will give acceptable results. There is a hearing-aid battery called Z675 which can be used. It is slightly smaller than the PX625, but it can easily be adapted to fit. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 12, 2005 - 11:35 am: |
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That's pretty evident for me. I found a Varta PX625 in the battery chamber which still had 1.35V. Swapped it with another known good Varta cell but had the same results. Also, as I mentioned, the meter is off in the lower region only. |
Mike
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 12, 2005 - 06:55 pm: |
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Hello Winfried-
The only repair information I've ever seen on the Uni/Auto 100 was in a 70's Camera Craftsman magazine which I was actually able to find around here. The article is extensive but makes no mention of adjusting the meter linearity or any circuit information at all. I guess that I would recommend scribing the VR and then moving it around to see what results. |
John Shriver
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 24, 2005 - 01:03 pm: |
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In a Topcon Super-D, there are two adjustment points for the meter. There is a selected resistor you can change, this changes the "slope" of the curve. (That is, how much the meter responds to one stop's worth of change of light. They called this "inclination".) The other adjustment, for meter sensitivity, is mechanical. The fine adjustment is by adjusting the pivot point on one of the rollers the chain that rotates the meter housing rolls over. The coarse adjustment is by the mesh of the gears that provide the coupling to the meter housing.
The chains in the Super D form the "analog computer" that takes into account the film speed, shutter speed, and lens aperture setting. Sort of computes the EV.
Obviously, the design of the Uni is quite different, since it's an auto-exposure camera. Still, letting you know how Tokyo Kogaku's engineers "think" may help you. It's a 50-50 shot whether that trimpot is the sensitivity, or "inclination". |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 25, 2005 - 02:08 am: |
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I am currently adjusting the meter. There is a small board with two resistors (connected in series to each of the CdS cells) and a variable resistor connected in parallel with the galvanometer. You can also turn the galvanometer against its base.
I found that the range of adjustment of the galvanometer is not sufficient in my case. I had to add one more resistor in series with the galvanometer to get a linear reading. I first connected another variable resistor and adjusted it to get a linear reading over the entire range.
So far, the meter now is consistent with my Gossen Profisix in the EV8 to EV16 range (at 100ASA the Profisix reads to EV18 only) within 1/3 f-stop.
The main difference between the Uni and other Topcon SLRs is that the Uni/Unirex use leaf shutters, controlled by a dial around the lens mount. So the linkage to the galvanometer base is quite different.
The Topcon Uni is built quite simple, just to avoid the word 'crude'. The auto-aperture mechanism is quite simple, there have been better designs in (viewfinder) cameras such as the Konica Auto-S2. |
