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Old 3rd Jul 2022, 5:31 pm   #1
EF80TVVALVE
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Default Ampro New Educational - motor woes, issues and solutions

Hi all

Some may remember we previously discussed the Ampro New Educational amplifier some time ago. At the time I was also having a problem with the motor, on the odd occasion it would drop in speed, almost stalling. A flick of the on/off switch usually had it back working okay. At the time giving a visual inspection I found there was a Hunts Mouldseal capacitor inside the motor itself and thought this to be the likely cause.

Fast forward a long time until today and I decided with a spare afternoon I should tackle this motor and get that capacitor replaced. After much frustration the motor was free, although still wired in to the projector. It's here that you have two options, either conduct what is equal to keyhole surgery on the motor to remove and replace the original capacitor or unsolder all motor wires and completely remove and fully dismantle the motor to gain good access to the motor.

Due to the design of the motor its impossible to lift the back housing clear of the spindle due to the internal wiring. To completely remove this the windings must also be loosened off and removed along with it. This is due to two carbon brushes that sit on the end of the motor body which make contact with a rotary centrifugal contact breaker for the speed regulator.

This speed regulator is where I found my next problem, the points have a lot of pitting so I had to remove and file back as much as I could, this still leaves a fair amount of pitting on the points but after several attempts of cleaning, refitting checking, removing, adjusting etc I now have the motor working relatively well, it still however runs a little uneven at times but no severe speed drop or stalling.

I'm now at the point where I know that any more rough running is due to this speed regulator which is somewhat unfortunate. I have tried scouring the Internet for ampro spares in hopes that spare breaker points are available, but it seems like none can be found.

The next thing is to see if this type of centrifugal breaker regulator can be serviced, ideally if anyone knows the actual name for this sort of speed control then that may lead me to the right path, alternatively I'll have to see what I can do with some breaker points for an old car and see if they can provide spares suitable to repair these.

Aplogies for the lack of photos, when I have the cover off again I'll add some to the post!
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Old 3rd Jul 2022, 6:11 pm   #2
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Default Re: Ampro New Educational - motor woes, issues and solutions

Many years ago, I used to have an Ampro, that I assume was similar to yours.
This also had the common problem of this type of centrifugal speed regulator acting directly on the the motor. (Nice smell though!)

Kenwood, on their very early food mixers used exactly the same system, & even with a capacitor / snubber across the contacts, they suffered a similar fate. Some early portable reel-to reel recorders also used the same method, only of course with a with a D.C. motor. Later recorders, used the same contacts, to switch a transistor, thus relieving the contacts of their inductive load.

If you are going to use this projector regularly, then I wonder if it might be possible to use a similar approach, only of course for A.C.
You could isolate the contacts, & use them to switch an electronic solid-state relay which in turn controlled the motor.

Just an idea of course, you may wish to keep it original.
I wish you luck with it.

David.
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Old 3rd Jul 2022, 6:58 pm   #3
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Default Re: Ampro New Educational - motor woes, issues and solutions

Thanks for your thoughts David, some things to think about. The only problem with any modification on these projectors is the tight space inside it, everything was designed to be as compact as possible and it can make repairs difficult.

I do wonder if I can make some replacement point contacts up and replace those currently fitted, another option is to try and find the Ampro part number for the points so I can see if any old stock exists anywhere. A third option is to file them down more which will probably reduce the thickness of the points by half.

It makes me wonder how many hours this projector has done, from appearance it looks to be relatively low hours but I suppose with proper care these machines can look so even with thousands of hours use.
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Old 3rd Jul 2022, 10:49 pm   #4
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Default Re: Ampro New Educational - motor woes, issues and solutions

If you want to keep origionality, I think you are stuck with a cacky motor. These type speed regulators were also used on early cassette recorders made in Asia.
If you want to use it as a projector, I would be looking for a motor of the same size designed for a "quadcopter ". These motors are three phase, very powerful, and need a speed controller regulator with them. The electric motors start with prices as low as $10 and a speed controller/regulator about the same. To have speed control and regulation you then add a "servo tester " which is just a squarewave oscillator with variable mark/space ratio. Total cost would be less than 20 quid. Oh, I forgot to mention, that under high torque these little motors can suck lots of current and need a decent power supply. The room you would gain by using such a small motor would give you the room for the extra "bits ".
So the pics show a motor and regulator, a full mounting kit ( which is supplied ) and a rule to give you some idea of size. This motor ( its a small one ) is 27.5mm dia. Its also external rotor. Under full power it can take 30 amps !!! at 12 volts. The speed controller is sized to suit. The one in the pic is labelled 30 amps. It will rev to about 8000 RPM,s and can go down to a few revs without cogging.
Its just an idea!.

Joe
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Old 4th Jul 2022, 12:19 am   #5
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Default Re: Ampro New Educational - motor woes, issues and solutions

Buried very deeply at Bedford I have a few spare centrifugal governor assemblies. I don't think there are any for Ampro, but if you can post a pic I might be able to recall. I make no guarantee of being able to retrieve them in any particular time frame though.

Last year I had to sort out the governors on a couple of GB 516's both of which had been interfered with. One had a mangled spring, the other had wrong screws etc. I've no idea why this had taken place, as both were capable of correct operation when reassembled properly. IIRC the contacts were in reasonable condition.
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Old 4th Jul 2022, 9:38 am   #6
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Default Re: Ampro New Educational - motor woes, issues and solutions

Joe, this is something to think about, it would be possible with some well thought modification. The original motor has a spindle through both ends so a similar motor would have to be sought, one end operates the cooling fan drum and the other drives the mechanism. I've never in the past had problems with these contact breakers but there's a first for everything.

Lucien, I'll take some photos of it as soon as I can. This example is a single breaker, I was looking at the 'Stylist' service info which has two breakers and in fact I think most 16mm sound projectors have two breakers, one for silent and one for sound. The motor speed arrangement of the New Educational means that the breaker is only needed for full speed sound films and silent is variable by a rheostat control.
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Old 4th Jul 2022, 9:49 am   #7
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Default Re: Ampro New Educational - motor woes, issues and solutions

I assume it's C23 we're talking about which is the 0.5uf across the governor contacts. The usual failure mode of these is short circuit: I was once watching a film on my Stylist when it suddenly speeded up to probably 48FPS until the film broke! These caps have a very hard life.

My New Educational has been fine so far, but still has the original cap AFAIK...

Stylist has two governors for 16 & 24FPS, Educational is governed at sound speed only.
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Old 5th Jul 2022, 8:06 pm   #8
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Default Re: Ampro New Educational - motor woes, issues and solutions

wd40addict, it's not C23, I already replaced that when I first bought the projector as it started shorting. The capacitor I am referring to is within the motor casing itself and is wired between the two brushes for the commutator. As far as I'm aware it isn't actually noted on the schematic. It's value is 0.05uf, different to C23 which sits inside the bottom of the projector and has a larger value of 0.5uF

Now I have the points cleaned and adjusted the best I can, I'm going to run it for a while and see if they bed in a little. The motor is now running correctly but there is noticeable drops in speed every now and then. Hopefully with some use a good contact will be made between the points and rid it of any need for more attention.
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Old 6th Jul 2022, 8:18 pm   #9
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Default Re: Ampro New Educational - motor woes, issues and solutions

Ok, so it's for suppression. Can't remember if I changed this on mine or not, but I don't hear any motor interference on my sound.

Regarding your speed dips is it worth temporarily bypassing the rheostat to prove its contacts are ok?

Are you also confident the rubber drive belt isn't slipping? I had real issues with mine.

Last edited by wd40addict; 6th Jul 2022 at 8:32 pm.
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Old 11th Dec 2022, 5:55 pm   #10
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Default Re: Ampro New Educational - motor woes, issues and solutions

Hi all, I'm resurrecting this thread as I've been spending some more time with the Ampro new educational. I've still got the motor speed dip which I'm still having trouble with. The belt on this was very tight and sticky, I've had trouble finding a replacement so for now I have lightly sanded back the inner face as this was covered in lumps of rubber that had collected in various patches. Once smooth I've rubbed a bit of talc on it, I know this sounds somewhat against the idea of a drive belt but it has solved the stickiness and the fit is overall much better. Unfortunately this hasn't solved the speed dipping so I can now rule out the belt.

The governer contacts are now nice and clean and show no resistance when closed. Interestingly I found that when the motor is ran with no load (ie no belt driving the main mech) it runs perfectly smooth.

From here I need to look in either direction. Is the motor having trouble with loading and causing it to run unsteady or is the mechanism slightly seized causing poor running? For a few hours (say 5) it has ran with no problems only for it to return. The hand turning for the mechanism leads me to think that it is nice and free but this could be different when running at full speed.
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Old 11th Dec 2022, 6:54 pm   #11
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Default Re: Ampro New Educational - motor woes, issues and solutions

It might be worth running for a while with the lamp off, so that any points that are suffering excessive or variable friction can make themselves known by their warmth.

Perhaps a max / min logging meter in series with the motor would give some clues. If the mech is binding then the slowing down will manifest as spikes in the current, but if something is intermittent in the motor or governor it will manifest as dips.
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Old 11th Dec 2022, 8:07 pm   #12
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Default Re: Ampro New Educational - motor woes, issues and solutions

Thanks Lucien, that's worth a go. I've been investigating more and really the projector mech is actually very nice and free, I now don't think this is at fault especially as it does this straight from cold. I do wonder if there is a break down in the insulation of the motor windings somewhere and the current draw when loading the motor is causing it to short and lose power. I have checked all physical contacts and connections and can't fault any of them so things are gradually pointing to this I feel.
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Old 11th Dec 2022, 10:17 pm   #13
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Default Re: Ampro New Educational - motor woes, issues and solutions

I can't fault your logic but hopefully it is not leading to the discovery of an armature fault, although it would be the most likely. They do tend to be accompanied by excess brush arcing and my hunch is that any fault serious enough to slow the motor down would cause at least a visible increase in what you see at the brush trailing edges, if not dramatic arcing.
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Old 17th Dec 2022, 4:16 pm   #14
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Default Re: Ampro New Educational - motor woes, issues and solutions

I've managed to get the motor out of the projector now and gave it a closer inspection. All of the windings look to be in excellent condition, there are absolutely no signs of overheating or burning which I was expecting. One thing I have found is that there are trenches between each contact of the commutator, on a lot of motors I encounter this is often filled with plastic or other material to give a completely smooth surface. As you can imagine each of these was caked full of old carbon deposits, I have cleaned this all out along with the rest of the motor and regreased. I am still in the middle of finishing off to refit so I hope that this has cured the problem and that it was due to tracking along the commutator contacts from all of the built up carbon.

Just a heads up, these motors are absolutely horrid to strip and clean! One of those where once the two main screws are out everything becomes loose and starts falling apart, it requires a lot of care to re-assemble with everything just in the right place as you begin to screw it all back up.
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Old 18th Dec 2022, 9:49 am   #15
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Default Re: Ampro New Educational - motor woes, issues and solutions

I seem to remember from my classic Mini workshop manual that the starter motor had the gaps in the commutator that you mention, but the dynamo was smooth. Or was it the other way round?
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Old 23rd Dec 2022, 5:20 pm   #16
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Default Re: Ampro New Educational - motor woes, issues and solutions

This is really the first time I've seen gaps in the commutator contacts, surely this would cause brushes to wear a little faster?

After much more fault finding it turns out that it is in fact the speed governor at fault at least the motor has been stripped, cleaned and relubricated, although it's somewhat frustrating that it's turned out to be something I was suspicious of but cast aside long ago.

This is where it gets a bit more difficult now, I have found a few suppliers of tungsten rivets or tungsten contacts that are brazed onto the points but there isn't actually any company that offers a reconditioning service. I could attempt this myself but there is a lot of room for error here so I'll have to do some thinking before taking the plunge.

The other alternative is if the governor can be replaced with a circuit to control the speed instead, this would be somewhat beneficial as there won't be any points giving trouble again.

For now I've sanded them back, they're working okay but I know that they won't last long before the fault returns, at least it will give me some time to work out my options!
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Old 23rd Dec 2022, 9:20 pm   #17
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Default Re: Ampro New Educational - motor woes, issues and solutions

Larger commutators, from an inch or so in diameter up to many feet, normally have undercuts between the segments. Without them, the more rapid wear of the copper relative to the mica would soon result in loss of contact pressure and excessively frequent skimming would be necessary to keep the micas flush with the copper, unless an excessively abrasive grade of brush were chosen. The mica is removed to a defined depth with a tool like a hacksaw blade with its kerf ground to the correct width. After undercutting, the comm surface is ground or stoned to leave a perfectly smooth edge that will not damage the brushes. The main disadvantage with the undercuts is their tendency to accumulate conductive paste if the machine runs in an oily environment.

Smaller, moulded micanite commutators vary. In some the segments stand proud of the moulding leaving the equivalent of undercuts, others are moulded flush to give a smooth cylindrical surface. On a small commutator of low peripheral speed that is not expected to run long hours, the relative wear rate might not be a problem, but there can be issues wth smearing of conductive deposits as there is no easy way for carbon dust, copper pickings, copper oxide and grit to escape from the face of the brush.

Can you re-purpose the contacts from car ignition points sets for the governor? I wonder whether it is possible to braze the ready-made tungsten-faced stud onto what you already have? Somwhere, buried deep, I have governors for B&H motors and possibly others, but I'm not hopeful that there would be any to suit your Ampro. If I can track the box down I will have a look.
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Old 24th Dec 2022, 8:14 pm   #18
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Default Re: Ampro New Educational - motor woes, issues and solutions

Thanks for the explanation Lucien, that sounds about right as most of the motors with a similar construction that I've stripped to clean have often been smaller than the one fitted into the Ampro which may explain why I haven't seen these small trenches between contacts. There are a few suppliers of either just the tungsten contacts themselves or the full rivet that can replace what is currently fitted. I'm sure the tungsten discs can be brazed to what is already there without much trouble and I could keep some spares for the future should I encounter the same problem. I bet reconditioning options haven't been around for a number of years as there can't be many motors plodding on with these types of governors fitted.

I could take some photos of the governor for you, I think the closest match may be from the Ampro Stylist which I believe had two sets for silent and sound, it's possible that they could be identical to the ones fitted to this model, just doubled up.
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Old 24th Dec 2022, 9:25 pm   #19
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Default Re: Ampro New Educational - motor woes, issues and solutions

Actually replacing the points by soldering on a new contact face is not as scary as it sounds.
I would be using silver solder though, not brass. Sufficient heat can be obtained from the small bench type blow torch that is filled from a cigarette lighter refill. Most of us probably already have one.
Then again, an ordinary SCR or Triac speed controller for a series motor might be the simplest.
I am assuming the motor is a series unit.
Once again, my original suggestion of a model airplane motor and controller is still viable and they are available with double ended shafts.

Joe
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