Minolta 7000: Memory backup lithium battery, main batteries, functionality, 7000 or 9000, disintegrated plastic, cleaning contacts, voltages

[Andreas Thaler]

Minolta Color Meter II

A few years ago I was able to have the device adjusted at a German repair shop that has since ceased business.

The color meter can be used, among other things, to measure the color temperature of the light and then adjust it to the slide film being used using light compensation filters.

 

[Andreas Thaler]

Maybe the device can also be used in the color darkroom?

 

[koraks]

Maybe the device can also be used in the color darkroom?

Maybe, although I don't really see how.
You could use it for its intended purpose, esp. together with a digital camera. Measure light temperature and set white balance manually on the camera.

The main question, however, is whether this meter will be any better than the automatic white balance adjustment in a typical modern digital camera. Frankly, I don't think so, and expect that e.g. a middle-of-the road DSLR will perform better and more consistently than this meter. A lot has changed in signal conditioning since these handheld meters were made. They use 1980s sensing technology and are prone to running out of calibration. Effects that easily throw off this kind of device (e.g. variations in ambient temperature, EMI) are much easier and more effectively mitigated in modern digital sensing circuits.

If you want/need a stand-alone color temperature meter, you can get a €2 Arduino Nano clone and a €5 RGB sensor off of AliExpress and build a meter that performs at least as well as this one in your attic/shed/living room.

Google Search

Adafruit_TCS34725/examples/tcs34725/tcs34725.ino at master · adafruit/Adafruit_TCS34725

Arduino library driver for Adafruit's TCS34725 RGB Color Sensor Breakout - adafruit/Adafruit_TCS34725

github.com

You don't even need to know how to write code. You can simply connect the modules together and run the example above. Hey presto - a working, calibration-free (actually auto-calibrating) color temperature meter.

 

[Andreas Thaler]

Maybe, although I don't really see how.
You could use it for its intended purpose, esp. together with a digital camera. Measure light temperature and set white balance manually on the camera.

The main question, however, is whether this meter will be any better than the automatic white balance adjustment in a typical modern digital camera. Frankly, I don't think so, and expect that e.g. a middle-of-the road DSLR will perform better and more consistently than this meter. A lot has changed in signal conditioning since these handheld meters were made. They use 1980s sensing technology and are prone to running out of calibration. Effects that easily throw off this kind of device (e.g. variations in ambient temperature, EMI) are much easier and more effectively mitigated in modern digital sensing circuits.

If you want/need a stand-alone color temperature meter, you can get a €2 Arduino Nano clone and a €5 RGB sensor off of AliExpress and build a meter that performs at least as well as this one in your attic/shed/living room.

Google Search

Adafruit_TCS34725/examples/tcs34725/tcs34725.ino at master · adafruit/Adafruit_TCS34725

Arduino library driver for Adafruit's TCS34725 RGB Color Sensor Breakout - adafruit/Adafruit_TCS34725

github.com

You don't even need to know how to write code. You can simply connect the modules together and run the example above. Hey presto - a working, calibration-free (actually auto-calibrating) color temperature meter.

My cameras are also from the 80s, that's all part of it.

 

[Andreas Thaler]

Battery holders: reworking the battery contacts

After bathing in Durgol descaling solution, rinsing with water and drying, there are deposits on the contacts damaged by the battery electrolyte.

It looks like light rust and can be removed with the fiberglass brush.

I will try to see if I can clean it with a plastic or brass wire brush on the Dremel Stylo.

If not, then I will try it with rust removal solution.

I see this for the first time when working with Durgol.

 

[Andreas Thaler]

I'm making progress with the plastic brush, the brass brush will be even more effective, but I can't get to the gaps.

So now it's time for the rust remover.

 

[Andreas Thaler]

The solution can be reused.

Let's wait and see what happens.

 

[Andreas Thaler]

Forgotten batteries in electrical devices can have terrible consequences: the battery electrolyte spreads through cables and circuit board conductors and attacks metals.

A process that progresses over years.

 

[ogtronix]

I see no difference in quality and workmanship between the 7000 and the 9000.

Both are heavy in the hand, plastic on the outside on a die-cast chassis on the inside.

I've been wanting to take a look at the 7000 for a while, but holding off in hopes of finding one cheap and attached to a lens I'd like. How do the buttons on it feel? Alot of articles/ reviews i've read claim the 9000's rockers are "a decent mid point between icky buttons and encoder dials" but i'm not sure if i'm convinced. I feel you could press buttons alot faster than sliding the rocker back and forth.

 

[Andreas Thaler]

I've been wanting to take a look at the 7000 for a while, but holding off in hopes of finding one cheap and attached to a lens I'd like. How do the buttons on it feel? Alot of articles/ reviews i've read claim the 9000's rockers are "a decent mid point between icky buttons and encoder dials" but i'm not sure if i'm convinced. I feel you could press buttons alot faster than sliding the rocker back and forth.

The buttons on the 7000 are small but well-built to fit the hand, the pressure point is reliable and firm.

I think the two pairs of buttons for time and aperture are a better solution than the 9000 with the sliding buttons, which I always press in the wrong direction or miss.

 

[Andreas Thaler]

It is also nice that at least I have never seen any dissolving and sticky light seals/mirror shock absorbers on the 7000 or the 9000.

Not even on the Canon T90.

In the mid-1980s, progress seems to have been made in this regard as well.

 

[Andreas Thaler]

After three hours in the rust removal bath.

That's nice now.

In the second picture above there is a spot of rust that I will work on with the Dremel Stylo.

 

[Andreas Thaler]

Rinsing in water and drying with the heat gun.

In the next step I'll take a close look at the contacts and see where I still need to rework them.

The question is how I can protect the damaged metal from further rust.

One possibility would be to apply conductive silver, but I don't know whether it can withstand high currents.

Ballistol universal oil should work, as it forms a protective film.

 

[Andreas Thaler]

There is even more rust here, I'll put the battery holders in the rust remover again overnight.

 

[Andreas Thaler]

Here is one of the battery holders that has been completely derusted.

Ballistol, applied thinly, spreads over the contacts and forms a protective film. It is also used for gun care.

I will keep an eye on it over the next few days to see if this continues or if rust forms again.


+++

All information provided without guarantee and use at your own risk.

 

[ogtronix]

The buttons on the 7000 are small but well-built to fit the hand, the pressure point is reliable and firm.

I think the two pairs of buttons for time and aperture are a better solution than the 9000 with the sliding buttons, which I always press in the wrong direction or miss.

Yeah, the 9000's rockers are really pretty weak. If it weren't for the bizarre quarter stop thing with the super program back i'd probably prefer its buttons.

 

[Andreas Thaler]

I don't know anything about the electrical properties of Ballistol and whether it acts as an insulator on the battery contacts.

You could recreate this in a test setup with a resistor as a load, but the batteries come with their current internal resistance (which increases with use) and I don't want to get involved in that.

So I'll be pragmatic and do a function test in the camera.

For the other battery holders, I'll spray the contacts with electronic cleaner, which also has a protective effect.

But perhaps the rust came from insufficient drying.

 

[Andreas Thaler]

Yeah, the 9000's rockers are really pretty weak. If it weren't for the bizarre quarter stop thing with the super program back i'd probably prefer its buttons.

For the 7000 you get the rare Program Back Super 70

Minolta Maxxum 7000 AF SLR camera - Part VI

 

[Andreas Thaler]

The battery holders have now been in the rust removal bath for 13 hours.

I am curious to see if the rust has completely dissolved.

 

[ogtronix]

For the 7000 you get the rare Program Back Super 70

Minolta Maxxum 7000 AF SLR camera - Part VI

Damn it even works with the CG-1000. I guess all the 9000 offers over the 7000 in the end is spot metering, multiple exposures, and the big heavy winders that probably run faster?

 

[Andreas Thaler]

Damn it even works with the CG-1000. I guess all the 9000 offers over the 7000 in the end is spot metering, multiple exposures, and the big heavy winders that probably run faster?

And a stop down button as well as shadow/highlight control and 1/4000 s as shortest shutter time, maybe more features?

Currently I have only found this offer for a Super 70:

Minolta Maxxum 7000 AF Film Camera Program Back Super 70 28-135mm 1:4 Lens | eBay

Minolta Maxxum 7000 AF Film Camera Program Back Super 70 28-135mm 1:4 Lens | Cameras & Photo, Film Photography, Film Cameras | eBay!

www.ebay.at

 

[Andreas Thaler]

The battery holders have now been in the rust removal bath for 13 hours.

I am curious to see if the rust has completely dissolved.

I see an improvement.

I will remove the remaining corroded areas after drying with the Dremel Stylo and the pointed probe.

 

[ogtronix]

Ah yeah the depth of field preview is a big one. Guess that doesn't make the 9000 seem as redundant. With the EOS cameras that lack a DoF preview it's pretty frustrating since the motor is in the lenses, but with how elaborate the system is on the 9000 for resetting the preview I can see why they'd omit it on the 7000.

 

[Andreas Thaler]

I was able to remove some more corrosion.

The finish is acceptable to me, what is important is that the corrosion has stopped and the battery holder conducts current reliably.

 

[Andreas Thaler]

Finally, I sprayed all the contacts with electronic cleaner, which also forms a protective film.

The excess spray evaporates and does not attack plastic.

Ventilate well.