Minolta (Maxxum/Alpha) 7000 AF: Aperture issues resolved/shortcut; LCDs, aperture ring, shutter unit replaced; aperture solenoid cleaned

ogtronix said:

How do the serial numbers of the two cameras compare? Like, I wonder if that was an earlier or later revision. It feels like it'd be earlier. But man there really is no way to clean that from outside.

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With cover on the solenoid and accessible contact surfaces, serial number: 19028546

This one: 22223124

I guess serial numbers are often encoded weird so its hard to tell, but that still might suggest it's a newer revision.

Troubleshooting according to C & C Associates Guide





There is no click from the solenoid, so I follow the instructions, check the voltage, continuity/resistance on the solenoid and replace it.

So take out the mirror box again

„Aperture magnet, SL-3 sticks causing mimimum aperture regardless of setting. You can try cleaning it, but its a long way back inside for a repair. I suggest you replace it.“ (ibid)

Click to expand...

I will follow this advice.

ogtronix said:

It's not corrosion it's the old 'anisotropic conductive film' breaking down. Isopropyl alcohol doesn't touch it. What worked for me was acetone, but be careful to keep it off the polarizing films on the LCD itself since it dissolves those.

Click to expand...

Just saw it in the C & C Troubleshooting Guide for the 7000.

The question is whether I can actually install the solenoids I have seen so far (see picture, please disregard both arrows) and I don't know the electrical values either. But a resistance measurement at the input of the two solenoids should provide clarity.

The input voltage for the solenoids is specified as „B+“ in the C & C Guide, which I read as the operating/battery voltage, i.e. 6 volts for all 7000. If that is the case, the solenoids should definitely be interchangeable as far as the electronics are concerned.

However, the 7000 has a built-in DC/DC converter, which means that a higher input voltage could be present. But that can be measured.

If the replacement magnet doesn't fit here, I may have to replace its mounting plate as well, etc.

Of course, the most beautiful of the 7000 gathering here is concerned …

As far as I can tell from my documentation photos, the mounting of the two types of solenoids is different, so an exchange will not be possible (please disregard the arrows):





Type A




Type B


Of the three possible errors mentioned above (diagram), only the third (solenoid stuck) is possible, as the solenoid was working before. Problems with the power supply or coil (continuity/resistance) are therefore ruled out.

I am almost relieved that I don't have to disassemble the 7000 again straight away

I will then see if I can find this particular solenoid in one of the eight 7000s that I bought as a bundle.

Where can I get a replacement for the aperture solenoid (magnet)?

Since, according to my observation, individual used parts for the Minolta 7000 AF are not available, the only option is to obtain them from discontinued 7000s.

It takes at least me about 1.5 hours to professionally disassemble a 7000 and dismantle the aperture solenoid from the removed mirror box.

For the process see



Faster but destructive disassembling without desoldering

You can of course also dismantle the 7000 destructively by separating the flexible circuit boards and cables with scissors and side cutters and only loosening the screw connections. This saves time, but irreparably destroys the spare part donor.


Determination and functional testing of the replacement solenoid

Beforehand, it is important to pay attention to which of the two known solenoid variants is installed because they are not compatible.




Easy removal of the top cover. Cables to the hot shoe do not have to be desoldered in this case.


This is easy with the 7000, you only need to remove the top cover to have a look.




Solenoid type A with plastic cover and accessible contact surfaces.




Solenoid type B without cover and not accessible contact surfaces.


If possible, the replacement solenoid should be checked for correct function before dismantling. This presumes that the donor 7000 can be triggered.

To do this, simply set one of the slower shutter speeds in M mode, mount a Minolta AF lens and set the available apertures in sequence. Observe from the front through the lens whether the apertures formed are plausible and formed evenly. Mode C is suitable for continuous motor drive operation.

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See also




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

Suitable agent for cleaning solenoids?

It may be that the electronics cleaner I used is not suitable for cleaning the contact surfaces of a solenoid because, according to the description, it leaves a protective film. This could prevent the solenoid from separating from its armature. However, this worked with the mirror magnet of the Canon T90.

The next time I try, I will therefore use isopropyl alcohol, which should not leave any residue. Or surgical spirit.

However, I would like to find a method to test the cleaned solenoid for functionality before assembling the camera. This should be possible by directly applying the intended voltage.

I will consult my technical documentation on this.

Alternatively I could measure the trigger voltage for the solenoid on a working 7000.

For this only minor diassembly is required.



The aperture solenoid connectors are accessible on the circuit board after removing the left front panel.

• Red arrow: positive connection
• White arrow: negative connection

Here I can use the oscilloscope to measure the voltage when the camera is triggered. It is best to use a longer shutter speed, which should produce a clear curve.

When the mirror box is removed, this part of the circuit board remains. To test the solenoid, I only need to unsolder the cables and connect them to an external voltage source with push button.

A new subproject that motivates me to take the 7000 apart again. Then I might not need a replacement for the solenoid if I get the existing one up and running again.

I'll continue on Monday.


+++

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

Testing the solenoid for opening and closing

To test the solenoid for opening and closing, I follow the instructions in the C & C Troubleshooting Guide. To do this, the white cable on the front circuit board needs to be connected to ground.

I do this with the battery holder attached and the main switch set to ON. There is no subtle clicking sound as stated, so the solenoid is not triggered.

Since I assume that the contact surfaces are contaminated, I remove the mirror box so that I can clean the solenoid.



First, I use the oscilloscope to measure the voltage on the positive contact of the solenoid against ground (bayonet ring), and then supply the solenoid with voltage via my laboratory power supply. The battery holder is then no longer connected to the mirror box.





6 volts DC against ground are present at the contact of the red cable, i.e. the full operating voltage (4 x AA).

This voltage is also present at the second contact of the solenoid (white cable). This means that current flows through the solenoid when the white wire is closed to ground.




The setup with the laboratory power supply. There is a push button on my experiment board with which I can trigger the solenoid when it is connected.






6.22 volt output voltage is available.




The mirror box is removed and the solenoid is connected to the laboratory power supply.








After a few activations of the button, the solenoid is triggered and the armature swings to the right with a quiet click.




From this I conclude that the solenoid is disconnecting unreliably due to contamination. I clean all contact surfaces with surgical spirit.




The solenoid is now separating properly.

I leave the mirror box removed and test it a few times to make sure that the solenoid remains in this good condition.

I observed the following at different voltages:

• 6.22 and 6 volts: solenoid triggers when button is pressed.
• 5 volts: same.
• At 4 volts and 3 volts the solenoid no longer closes.
• At 0 volts it closes.

This would mean that there is no permanent magnet built into the solenoid, but rather an iron/steel core that becomes an electromagnet when exposed to voltage. The armature separates when this voltage is short-circuited.

This corresponds to the observation at the beginning that the operating voltage is permanently applied to the solenoid. Consequently, a sufficiently strong magnetic field cannot be formed at 4 and 3 volts to hold the armature.

However, the armature holds at 0 volts, which I explain with residual magnetism in the core.

Whatever the case, the only important thing is that the solenoid works when in operation.

The solenoid is still working perfectly, so I'm putting the 7000 back together and hope it stays that way.

If that doesn't work, I can use the C & C Troubleshooting Guide to troubleshoot further. It could also be that the electronic control for the solenoid via the camera circuit is not working. But I don't think so, because the solenoid was working to begin with, albeit unreliably.

We'll see.

No success

The reassembly worked but the 7000 still closed to the smallest aperture.

Following the C & C troubleshooting instructions, I tested the aperture solenoid from the outside and it worked. This means that the cleaning was successful if it was actually contamination.

Using the oscilloscope, I measured different measuring points in the circuit as per the instructions and ended up with three possible errors:

1. Two-layer contact open,
2. a pin on an IC not soldered or
3. one of two ICs defective.

I opened and checked the two-layer contact, cleaned the contacts, replaced the pressure plate with a rubber pad and put a second one on top to increase the pressure.



That was probably too much and the 7000 was left with a blocked gear and the display no longer shows anything. I probably damaged the flexible circuit board.

But that meant I had exhausted all options.

One of the mentioned ICs is on the underside of the circuit board above the prism and I would have had to take the camera apart again to check it. Beside this replacing ICs is not an option for me with these cameras, it doesn't work.

But it wasn't in vain, I learned a few things and spare parts in very good condition are always welcome

This project is now complete.

Of the seven 7000, four are working and three are happy to supplying spare parts.


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

Post note:

When testing the solenoid in the manner described, you should only send current through it for a very short time so as not risk to overload the fine copper enamel wire in the winding.

Here you leave the manufacturer's circuit and what you do is based on your own considerations. These may or may not be correct.

This is all the more true:

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

Due to the numerous accesses to this thread, here are related recent topics about the Minolta (Maxxum/Alpha) 7000 AF on PHOTRIO:

Andreas Thaler said:

No success

The reassembly worked but the 7000 still closed to the smallest aperture.

Following the C & C troubleshooting instructions, I tested the aperture solenoid from the outside and it worked. This means that the cleaning was successful if it was actually contamination.

Using the oscilloscope, I measured different measuring points in the circuit as per the instructions and ended up with three possible errors:

1. Two-layer contact open,
2. a pin on an IC not soldered or
3. one of two ICs defective.

I opened and checked the two-layer contact, cleaned the contacts, replaced the pressure plate with a rubber pad and put a second one on top to increase the pressure.

View attachment 391489

That was probably too much and the 7000 was left with a blocked gear and the display no longer shows anything. I probably damaged the flexible circuit board.

But that meant I had exhausted all options.

One of the mentioned ICs is on the underside of the circuit board above the prism and I would have had to take the camera apart again to check it. Beside this replacing ICs is not an option for me with these cameras, it doesn't work.

But it wasn't in vain, I learned a few things and spare parts in very good condition are always welcome

This project is now complete.

Of the seven 7000, four are working and three are happy to supplying spare parts.


+++

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

Click to expand...

Electronic error fixed: It's going on again

Today I took another look at this 7000 AF, which was no longer showing any signs of life.

In the C & C Troubleshooting Guide I followed a check instruction under „Power Circuit Malfunctions".




When the top cover with the slider for the main switch is removed, these two contacts are bridged (red jumper wire) and the 7000 is on.

Before soldering the protective varnish over the contacts must be scraped away.


It started with checking the battery input voltage on the circuit board, i.e. the direct connection to the battery.

At the two soldering points of the red and black cables on the bottom circuit I measured 1.4 volts, it should be 6 volts.

A check with the continuity tester on the multimeter showed that the black negative cable had a resistance of around 1 kiloohm. It should be 0 ohms.




Broken fuse.


I set about checking the cable, checked the connection on the battery compartment and finally found the cause of the error. A fuse consisting of a fine wire had broken. The foam underneath was still conducting electricity and this was how the resistance came about.

Around 4.6 volts of the battery voltage dropped across this resistor. That explained the low input voltage of 1.4 volts at the circuit board (see equivalent circuit diagram below).




Bridging with jumper wire (white arrow).

Since I was too lazy to set up my soldering station, I used the cordless soldering iron with the wide soldering tip. A dent had already melted into the plastic


I did not know why the fuse had melted. So after a check of the upper board where I had worked some days before I took a risk and bridged the two fuse terminals with jumper wire.




The 7000 AF is back to life.


There is no longer a fuse, but nothing burnt when attaching the battery holder, the 7000 is back in good shape

So I'll continue here as soon as I have a suitable replacement for the aperture solenoid.

Equivalent circuit diagram

For visualization here is an equivalent circuit diagram for this error in the power supply:

• 6 volt battery voltage.
• In front of the negative pole of the 4 x AA batteries there is a resistor of 1 kiloohm (conductive foam which is supplied with voltage by the two fuse terminals).
• The resulting internal resistance of the batteries is 304 ohms.
• The output voltage on this unloaded voltage divider is 1.4 volts, which I measured at the input of the board.

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This equivalent circuit diagram is not about exact values, but rather an explanation for the problem.

Of course, you can do without it and simply fix the fuse.

But the more you understand, the better equipped you are for electronic troubleshooting.


It would be interesting to know

how the fuse overloaded.

If the reason was a short in the circuit, the consequences of which were prevented by the fuse, the bypass would not help. It would only ensure that one or more components in the circuit were overloaded or even destroyed by the short.

Here I simply took a risk and was obviously lucky.

Beforehand, however, I checked the area of the circuit board I had been working on for damage, but found nothing.


+++

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

Adjusting the curtain speeds of the Copal S shutter on the Minolta 7000 AF,

see

Post in thread 'Copal S(quare) Shutter: Testing when removed?'
https://www.photrio.com/forum/threads/copal-s-quare-shutter-testing-when-removed.212393/post-2879226

If we assume that the aperture problems on the 7000 AF are caused by the malfunctioning aperture magnet, it's probably better to replace the magnet. Larry Lyells also recommends this in the C & C Troubleshooting Guide.

Why cleaning the contact surfaces isn't reliable in this case remains a mystery. Perhaps the magnet changes its properties over the decades; I don't know.

Replacements are inexpensive to make from other 7000 AF cameras where the magnet is working.

One guess as to why the 7000 AF is permanently set to the smallest aperture:

There was apparently an overload in the circuit, which caused the fuse to blow.

The overload could have previously damaged the winding on the aperture magnet.

This prevents a temporary magnetic field from being created that would neutralize the permanent magnet and trigger the aperture lock to the intended value.

In this case, the winding would have to be high-resistance if it were blown and the magnet has to be replaced.

It's on my list for checking.