Minolta MD-90, BP-90 and AW-90: Test, troubleshooting contact problems, dissection

[Andreas Thaler]

Today I achieved my goal of putting together two functional units, each consisting of a Minolta 9000 and a Motor Drive MD-90 with a BP-90 battery holder.

It was also an eventful session:

• One of my six working 9000s failed.
• I was able to add a working Winder AW-90 to my ensemble and
• I dismantled a damaged MD-90 to try to repair it.

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MD-90 and BP-90: Troubleshooting contact problems

I bought two pairs of motor drives/battery housings with battery holders on eBay and unpacked them today.

A third motor drive was already there.

I started preparing for tests on three 9000s.

Cleaning the numerous contacts with electronic cleaner.

12 x AA batteries provide 18 volt operating voltage for the motor drive.

The operating voltage is fully available both at the battery holder and at the output on the housing which provides voltage to the motor drive.

Cleaning contacts on the 9000 and MD-90.

The motors work, but there are interruptions when the motor drive and battery housing are moved on the 9000. The motor drive/battery housing unit wobbles a little on the camera.

Further treatment with electronic cleaner did not bring any improvement.

After I had machined the partially corroded/dirty motor contacts on the 9000 with the smallest milling head on the Dremel Stylo, the contact problems were almost completely resolved.

The contacts are recessed in a plastic holder on the base plate of the 9000. The milling head rubbed off some of the surface of the contacts without milling.


Loss of a Minolta 9000

The third 9000 jammed during motor operation and the shutter could no longer be cocked.

Resetting the mechanism via the base plate did not work.

There is nothing I can do about it.

Given the complexity of the camera, I have ruled out dismantling the 9000 to find the fault.

Game over

 

[Andreas Thaler]

Disassembly of a damaged Motor Drive MD-90

One of the three MD-90s had obviously experienced violence and also had a mode dial that no longer clicked into its positions.

The motor worked, but I still opened it to repair the mode dial.

Here the upper cover plate is warped.

The mode dial is on the right.

The front panel is clipped in and stuck tight. When I tried to remove it, two plastic tabs broke.

I was able to remove the dial, but the mechanism with the catch is located under a cover that is riveted to the plastic plate. I can't get to it without damaging it.

Since I already have two working MD-90s, I gave up on repairs and made a dissection instead. This gives me insight and spare parts remain.


Here are some impressions from a complex and high-quality manufactured motor drive:

The contacts under the mode dial.

The housing is made of plastic.

When lifting out the motor unit, the lock for the battery housing must be overcome.

An electrolytic capacitor that does not leak.

A DC motor from Copal, manufactured in 1985 according to the sticker.

 

[mshchem]

Too much plastic for the era.

I'm always interested in your work.

I would submit for your consideration, a CLA and refurbishment of a Hasselblad A12 back. I have "repaired????" a couple of these by a few drops of lighter fluid, and put in a couple light seals. I've never tried a real CLA.

Best Regards Mike

 

[Andreas Thaler]

When I opened the case, and I was careful, these parts came out.

An intermediate result:

• two working MD-90/BP-90 units,
• one failed 9000 and
• one dissected MD-90.

Winder AW-90

With a functioning Winder AW-90, whose battery compartment lock I had previously replaced, I end the day with a positive result

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Conclusion

• All the devices shown are of high quality.
• The motor drive MD-90 with battery housing BP-90 (12 x AA) makes the 9000 a heavyweight. But an additional portrait format shutter release, four motor settings and a setting for AF focus priority are the reward.
• The numerous contacts on camera, motor drive and battery housing are very sensitive and have to be perfect so that there are no interferences.
• I cannot say whether the 9000 fell victim to the motor drive.
• The winder AW-90 is much lighter with 4 x AA batteries and offers single/continous/focus priority mode. A good alternative if you do not need the high motor frequency.

+++

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

 

[Andreas Thaler]

Too much plastic for the era.

But used sensibly.

I'm always interested in your work.

Thank you

I would submit for your consideration, a CLA and refurbishment of a Hasselblad A12 back. I have "repaired????" a couple of these by a few drops of lighter fluid, and put in a couple light seals. I've never tried a real CLA.

I don't know anything about that.

But you could start a thread about it, it would be interesting in any case!

 

[ogtronix]

The separate focus priority switch on that AW-90 is interesting. I think that's something really lacking from the MD-90, the way it only lets you do focus priority on continuous mode. Makes me wonder if you could maybe modify it to operate FP on single shooting mode, or with its own bodged in switch... You can sort of do that by removing the battery with it set to FP mode and manually advancing between frames. Poking at the contacts that join it to the body with a multimeter doesn't suggest it's as simple as it just shorting a couple pins there.

The BP-90m I have was pretty trashed inside from leaked cells.

I didn't take particularly good pictures of disassembling it. The main things I remember were screws hidden under the bottom plastic sheet that has to be peeled off (it doesn't crease easily at least, and the adhesive is good to just stick it back down), there's a sneaky screw hidden down next to the battery contacts inside the thing, I didn't take note of the battery latch spring before it fell out and had to figure out how it goes back in, some of the wire ends were super brittle from contact with electrolyte so it's probably worth taking note of what goes where as soon as possible, there's a flat cable adhered to the inside (connecting the pads for the flash bracket) that's probably better just peeled off than trying to carefully work around (plus the traces were rotted at the ends and needed reconnecting on this one), and it might be worth wearing gloves since it's from the era of mercury in cells. There's a couple fine wires along the length of it that're easy to pinch on reassembly too, leading to the case not closing entirely flat.

 

[Andreas Thaler]

The separate focus priority switch on that AW-90 is interesting. I think that's something really lacking from the MD-90, the way it only lets you do focus priority on continuous mode. Makes me wonder if you could maybe modify it to operate FP on single shooting mode, or with its own bodged in switch... You can sort of do that by removing the battery with it set to FP mode and manually advancing between frames. Poking at the contacts that join it to the body with a multimeter doesn't suggest it's as simple as it just shorting a couple pins there.

The BP-90m I have was pretty trashed inside from leaked cells.
View attachment 387519 View attachment 387524 View attachment 387525 View attachment 387526
I didn't take particularly good pictures of disassembling it. The main things I remember were screws hidden under the bottom plastic sheet that has to be peeled off (it doesn't crease easily at least, and the adhesive is good to just stick it back down), there's a sneaky screw hidden down next to the battery contacts inside the thing, I didn't take note of the battery latch spring before it fell out and had to figure out how it goes back in, some of the wire ends were super brittle from contact with electrolyte so it's probably worth taking note of what goes where as soon as possible, there's a flat cable adhered to the inside (connecting the pads for the flash bracket) that's probably better just peeled off than trying to carefully work around (plus the traces were rotted at the ends and needed reconnecting on this one), and it might be worth wearing gloves since it's from the era of mercury in cells. There's a couple fine wires along the length of it that're easy to pinch on reassembly too, leading to the case not closing entirely flat.

I had tried to open one of my two BP-90s because I thought that I could bend the contacts for the output voltage better that way, and of course I was curious.

But after loosening all the visible screws, including the one inside the battery contacts, I couldn't get any further.

And then I stopped so as not to endanger the battery housing. They are rare, as I have seen.