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

[Andreas Thaler]

Test with batteries: 4 x AA and 4 x AAA

Both battery holder types each deliver identical output voltages, which are plausible.

Remove the batteries from the battery holders without damaging your fingernails.

Helpful tool to remove batteries

Because I no longer wanted to break my fingernails when removing AA batteries from battery holders and battery compartments, I found help in my toolbox. With this tool, AA batteries can be easily grabbed and pulled out or levered out. It is a desoldering lever that is intended for...

www.photrio.com

 

[Andreas Thaler]

Excursus: measured voltage on the battery holder and its significance

I was still thinking about what the measured output voltages of around 6 volts on the battery holders mean for practical operation.

Is that really the input voltage that reaches the circuit of the camera?

I only measured the unloaded open circuit voltage.

And what if corrosion on the contacts of the battery holders leads to a reduction in current flow? This would reduce the input voltage by adding resistance to the internal resistance of the batteries connected in series.

Here are two equivalent electric circuits to answer these questions.


Output voltage at the battery holder outside the camera

From bottom to top:

• ground
• Four AA/ASA batteries connected in series with 1.5 volts each = 6 volts.
• Internal resistance of the batteries, here set at 50 ohms.
• Resistivity due to reduced conductivity of the contacts (corrosion) set at 25 ohms.

Here you can see that, despite the two resistors, the output voltage (open circuit voltage) is equal to the battery voltage. Both resistors are at the potential 6 volts.

This is the voltage that I measured on the battery holders.


Output voltage at the battery holder in the camera

Here is the equivalent electric circuit for a battery holder that is inserted into the camera, the camera is turned on.

The structure is the same as the circuit above, with the resistor of the camera circuit added as a load on the right (1 kiloohm, all resistances as assumptions).

Now you can see that the input voltage on the camera (terminal voltage) is 5.58 volts, which is about 0.5 volts lower than on the battery holder, which is not inserted in the camera.

The reason for this is the internal resistance of the batteries and the resistivity due to reduced conductivity of the contacts (corrosion) at which voltage drops.


Conclusion

This means that measuring the voltage directly on the battery holder is not meaningful.

How can I test whether the battery holder is working properly?

This can be done with a continuity test.

This measures whether the connected lines in the battery holder have a resistance close to 0 ohms, which means that the current can flow almost unhindered.

The problem with these battery holders is that the wiring is partly not visible because it is under the cover and I don't have a circuit diagram.

This means that we can only make assumptions about the current flow.

I won't go for that, but will test the battery holders on the camera. In the hope that everything is OK

So why do you check the open circuit voltage on the battery holder? To determine if the wires are unbroken.


+++

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

 

[Andreas Thaler]

Removing the decomposing plastic coating on the battery compartment BH-70S and handle

The plastic coating on the battery compartment for 4 x AAA batteries as well as on the handle of the 7000 can crack and break off.

Reconstructing the gaps with Sugru only partially solves the problem, as it does not fix the remaining plastic.

As with the Minolta 9000 AF, the plastic coating can be easily removed. This should not affect the functionality of either camera.

I removed the plastic from one of my 7000s with a BH-70S battery compartment.

The three spudgers from iFixit are ideal for this job. They are made of plastic and allow for gentle removal.

The plastic parts can mostly be removed quickly and without effort.

The handle of the 7000 without plastic cover.

Direct view of the circuit board. I will cover this hole with Sugru.

There is also plastic inside the battery compartment that can come loose. Here you can also see the circuit board, but this has no further effect as the battery holder is located here.

Here, too, there is a gap that can be closed with Sugru.

What remains is - depending on your point of view - a cosmetic problem.

I'm leaving my 7000 in its original condition and will not make a new cover.

 

[Andreas Thaler]

Plenty of plastic waste.

Another small optical improvement.

I recommend wearing safety glasses when working, as the plastic parts are brittle and have sharp edges and can fly off when lifted off.


A few words about user and camera safety

If this metal part is connected to the camera chassis, it should be electrically at ground potential. As is most likely the tripod screw.

This should not cause any malfunctions when touched, but it is something to be aware of.

With an operating voltage of 6 volts, I do not see any safety risk for the user or camera, even with wet hands, as the metal part is not expected to contact the positive pole of the battery holder, which has the higher potential. And even then the circuit must be closed to ground so that current can flow.

But if an electronic flash, which generates dangerously high voltage, is mounted on the camera, things may be different. But here too the flash would have to have a faulty connection, etc.

In any case, the camera no longer meets Minolta's original standards and these are just my assumptions.

I am always very careful with electricity and anyone who does it, as I have done here, does so at their own risk and responsibilty.

+++

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

 

[ogtronix]

I ran into these 3d models for some replacement grip plastic. There's also this guy's rechargeable one which looks alot nicer in that commercial SLS surface finish than the goopy stair-stepped FDM style. It's probably grippier too.

Also that electrical safety thing reminded me of a story I read on an machining forum years back where a guy got his wedding ring between the positive of the car battery and the negatively grounded chassis, which rapidly heated it. He was okay but never found the ring again after flinging it off his finger and into a field.

 

[Andreas Thaler]

Also that electrical safety thing reminded me of a story I read on an machining forum years back where a guy got his wedding ring between the positive of the car battery and the negatively grounded chassis, which rapidly heated it. He was okay but never found the ring again after flinging it off his finger and into a field.

Even AAA and AA batteries should not be underestimated. In the event of a short circuit, high currents flow and things get hot quickly.

 

[Andreas Thaler]

I ran into these 3d models for some replacement grip plastic. There's also this guy's rechargeable one which looks alot nicer in that commercial SLS surface finish than the goopy stair-stepped FDM style. It's probably grippier too.

Thanks, that's interesting, I'll take a look.

But I'd have to start printing it myself.

Where can I get it done?

 

[ogtronix]

Going entirely by Youtube sponsorships, because I guess advertising works even if I hate to admit it, there's Shapeways and PCBWay. There's also JLCPCB which i've used a few times for PCBs and it seems they offer a 3d printing service as well. There's probably a bunch more. I did a quick search for others but only found companies offering FDM, which is the style with ugly layer lines... although you can sand, fill, and paint them.

 

[Andreas Thaler]

Going entirely by Youtube sponsorships, because I guess advertising works even if I hate to admit it, there's Shapeways and PCBWay. There's also JLCPCB which i've used a few times for PCBs and it seems they offer a 3d printing service as well. There's probably a bunch more. I did a quick search for others but only found companies offering FDM, which is the style with ugly layer lines... although you can sand, fill, and paint them.

Thank you, I will have to deal with this new world of printing art