How to calibrate light meter in Minolta Hi-Matic 7 Sii?

[Businessfotos]

Hi all, I have a Minolta Hi-Matic 7 Sii which I got recently. I need to calibrate the meter which is off. I run the camera with hearing-aid-battery 1,4V. So I opened the top cover and discovered a potentiometer at the back of the meter unit. I tried to calibrate/adjust the measurement with different light situations and different ISO values comparing it to a reliable light meter. I was able to get a decent adjustment for mid/high-lit sight situations but it's still off in dim light. Seems like a non-linear error. The other thing is, I needed to crank the potentiometer all the way to one side to achieve these decent results. Does all this simply mean that the light meter is too old to adjust? It there more to calibrate it than the potentiometer? Is it because of 1,4 vs. 1,35V?
Your help an input is appreciated ;-)

Greets, Till

 

[xkaes]

It's been a while since I used a 7sII, but I know that different cameras designed for 1.35v batteries respond differently to batteries with different voltages. And I get the impression that voltage is not the only factor of the battery that can make a difference. Lots of people have had good enough luck by simply adjusting the ASA -- but how much to adjust depends on the camera and the battery.

 

[Ricardo Daniel]

I found this in internet: "The meter has two adjustment resistors. Right one is connected in series with a galvanometer. It adjusts linearity of a response function by rolling its upper part (higher EV) down. Left one shunts those two forming a current divider. Use left one if you need a more or less constant EV bias. It also can be used to readjust a meter for a different battery voltage.".
I have a Minolta Hi Matic 7Sii with 2-3 stops underexposure (depending on actual situation), I tried using hearing aid batt (1.4V) but not big difference.
I checked the metal plate on front CDS but it is ok. I also checked the batt contact on the lower side but it is ok, I really do not know how it could have so big underexposure but calibrating the resistors I think it is the solution. There should be 2 of them, no idea where are they located. Look like you found one.

 

[ant!]

I can't add something to the actual calibration, but I just used a few weeks ago a Hi-Matic 7sII with a hearing aid battery. I tested it roughly against a white wall with another light meter, and it was pretty ok, so I used that without any adjustements. I did not test nonlinearity. I shot a film (expired color negative with a bit over-exposure). I just scanned the negatives (but didn't invert them yet), but as far as I can tell, the negatives look ok to me (of course, expired film and high-tolerance C41 film are not precise measures). So, as far as I can say, my camera seems to be fine with hearing aid batteries...
(but I have 2-3 shots midroll with double exposures, I guess I just banged the unlock button underneath accidentally a few times or it needs some cleaning, but of course it could also be a film advance issue, even though the spaces look fine in general, and these double exposures are really in the middle of the roll...)

 

[4season]

CdS photo resistors can and do fail sometimes, and I suspect that's what you're dealing with.