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Repairing old Super-8 camera - DC motor requires help to start

SpookySnek

Jun 13, 2024
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Hello guys!

I am currently trying to repair this old Super-8 camera (Agfa Microflex 300).

After cleaning and fixing a connection that was broken due to battery leakage, the camera now seems to work as it should, with one caveat: I need to push the gears forward "ever so slightly" to make it actually start moving. I've lubricated the gears and shafts to no avail. I've cleaned the contact points that switch on the motor. I've tried adjusting the variable resistors one by one, not really knowing what most of them does.

The motor is a 3V DC motor and receives around 2.8V. I've tried to find info on the "NEC MC-5059" IC to no avail. I've also tried to find a service manual or something of that nature with explanations for the PCB and components, but it doesn't seem to exist anywhere on the internet.

I think that my next step will be to replace all the capacitors with new ones in hopes that at least one of them is used to "kick start" the motor, although my electronics knowledge is way too slim for me to see which one of the caps that could be used for this, if any. Could it help? Hopefully my conversion of the color codes is correct, it does seem to be very low values though.

I also plan on replacing the old "STABILYT 12" 1.5v battery cell with diodes + a cap (found a solution in an obscure german vintage radio forum), I do believe this is only used for the light sensor though.

The second motor (the one next to the lens, "outside" of the camera body) is used for zooming and works fine.

Any help at all that could lead me in the right direction would be greatly appreciated!! <3
 

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Bluejets

Oct 5, 2014
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Tantalum caps do not go bad like electrolytics, they merely go bang.
When you say motor is 3v yet only gets 2.8v, it appears that may be part of the problem.
Brushed dc motors DO get dirty on the commutator so that would be my first bet.

What cells are recommended originally and what are you using now?
Dry alkaline should have a start out pd up around 1.6v each at least.

https://en.wikipedia.org/wiki/Alkal...al voltage of a,zinc oxide in the electrolyte.
 

SpookySnek

Jun 13, 2024
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Tantalum caps do not go bad like electrolytics, they merely go bang.
When you say motor is 3v yet only gets 2.8v, it appears that may be part of the problem.
Brushed dc motors DO get dirty on the commutator so that would be my first bet.

What cells are recommended originally and what are you using now?
Dry alkaline should have a start out pd up around 1.6v each at least.

https://en.wikipedia.org/wiki/Alkaline_battery#:~:text=The nominal voltage of a,zinc oxide in the elect
Thanks!
I'm using new alkaline batteries and have tried rechargeable AAs too, which I do believe should work for this camera. Unsure if they recommended a certain chemistry originally though.

I did actually try replacing the caps yesterday but it didn't make any difference.

I think that the motor could be the culprit just like you're saying. I took out the motor yesterday together with a motor from a donor camera of the same model (with extensive moisture damage). I'll attach a picture, the left one is the motor from my donor and the right one is from the camera I'm repairing. I do like the funny little window that the right one has lol.

Anyways neither of them seems to start spinning off of 2 AA batteries, even without load, until I "help them" ever so slightly. So I guess that either I somehow repair one of them, or I just try to source a new one. I'm not sure how I would go about sourcing a matching motor though, I can't find any info on these and they seem to be of a bit of a funny size, 35mm long (without axle) and ~19mm width. Since I couldn't figure out how to tune the camera speed using the trimpots/variable resistors, I think I'd need a motor with similar characteristics that doesn't require much tuning.

Now I'm one step closer at least maybe?
 

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Bluejets

Oct 5, 2014
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Ni-cads and Nickle metal are lower pd which is why I asked.
If you have problems with a motor starting on fresh alkaline cells, the former will not help , only make matters worse.

Motor speed could be anything and without any working reference, impossible to say.
One thing is for certain, replacing a dodgy motor with another dodgy one is not a step closer by any means.

It appears the one motor with the "window" may be showing a manual speed regulator adjustment.
If this is the case, it is possible that dirty or contaminated points on this "regulator" could be where you are getting a voltage loss.
 

SpookySnek

Jun 13, 2024
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Ni-cads and Nickle metal are lower pd which is why I asked.
If you have problems with a motor starting on fresh alkaline cells, the former will not help , only make matters worse.

Motor speed could be anything and without any working reference, impossible to say.
One thing is for certain, replacing a dodgy motor with another dodgy one is not a step closer by any means.

It appears the one motor with the "window" may be showing a manual speed regulator adjustment.
If this is the case, it is possible that dirty or contaminated points on this "regulator" could be where you are getting a voltage loss.
One step closer in the sense that I at least seem to have nailed down the culprit haha.

I actually just got one of the motors to work from start by cleaning and messing with said adjustments through the "window" (the other motor actually had a window too, hidden behind the sticker). The bad part though; It still has a very small "dead zone" where it simply will not start spinning on its own, and it seems to be due to normal wear. The contact points are not carbon brushes, just simple springy copper plates... So it indeed seems to be time to source a new motor. I tried to calculate the rpm using using this method, which obviously isn't very exact by any means, but it seems to be spinning at around 5500rpm.

I'll try to find a close-ish match and see what kind FPS I end up at. Even though a 60FPS super-8 camera sounds cool, I'd rather not use a full $50 cartridge in 20 seconds
 

Bluejets

Oct 5, 2014
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The bad part though; It still has a very small "dead zone" where it simply will not start spinning on its own, and it seems to be due to normal wear.
That would be due to either a fault on the commutator or a bad armature coil.
 

SpookySnek

Jun 13, 2024
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That would be due to either a fault on the commutator or a bad armature coil.
Yes, there seems to be pretty extensive "grooves" in the commutator together with a few deep scruff marks that create friction. So you're likely correct!
 

73's de Edd

Aug 21, 2015
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Yes, there seems to be pretty extensive "grooves" in the commutator together with a few deep scruff marks that create friction.
1720354091491.png




This uses 3 segments . . .but . . . if yours only uses a single leaf segment , lateral brush repositioning to land on a clean commutator area might work.
Also, can you trace the power line from the the hot wire of the motor, to where it gets switched on . . . possibly thru a switch or relay ?

If so, then temporarily wire in a 5000 + or so ufd /5v capacitor on that other power side so that it can get charged up, yet, be isolated from the motor until the motor gets switched to turn on.
And then when motor power gets switched on, that extra short time BURST of the caps reserved supplemental stored energy might just be enough to get the initial BOOST to get rotation of the motor . . as its all being downhill after that initial start up requirement.

It still has a very small "dead zone" where it simply will not start spinning on its own,
That sounds like an open armature winding or more likely dirty oxidized commutator contact segment.
With no batteries in the unit for a no power situation, ohm out those segments.
They will be paired up 180 degrees apart . . . . just as the mating brush connections are.
They will be low ohm and expect the problem " dead" segment pair to read open.


73's de Edd . . . . .
 
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