8mm Forum: GS1200 Motor (Electrical Noise)

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Posted by Paul Adsett (Member # 25) on September 23, 2017, 03:15 PM:

I am getting electrical noise from the front reel motor being picked up by the amplifier. It is present all the time when the projector is running in forward mode and can be heard on silent areas of the film.
Anybody have any advice on possible fixes?

Posted by Steve Klare (Member # 12) on September 23, 2017, 03:26 PM:

It sounds like worn brushes to me. I had something similar from the transport motor on one of my ST-800s a few years ago. I could pick up the interference with an AM radio anywhere in the house and as locally as the heads were to the motor it came through loud and clear through the machine's speaker.

Posted by Andrew Woodcock (Member # 3260) on September 23, 2017, 03:26 PM:

Strange one that Paul if I'm understanding correctly as the front reel motor won't even be energized while playing a film? [Confused]

Posted by Graham Ritchie (Member # 559) on September 23, 2017, 04:06 PM:

Thats an interesting one Paul [Roll Eyes]

both the rewind and take up motors "both" run when fwd is pressed they have to. How is the film tension on play on the feed arm, as that fwd rewind motor has to be running? I cant imagine the motor itself causing the electrical noise, its such a small motor with only two tiny brushes in it as in the past I have had them apart. You could try earthing the motor, or pull it apart in place which is easy to do and clean the commutator with some fine wet and dry then gently scrape with a craft knife the build up of "deposit" between each of the segments on the commutator...finish with a wash with CRC Electra clean or something like that and see what happens. Those dinky little take up and rewind motors do get gummy over time.

PS...just a thought [Roll Eyes]

I know when I use the rewind on film I get a crackle from the amp. Once I push fully in that rewind buttom when I am finished and press fwd I dont get any. I wonder if there is something going on there, that causes what you get on rewind to get fed through on the fwd. It might sound silly but is your rewind button fully in.??

[ September 23, 2017, 05:12 PM: Message edited by: Graham Ritchie ]

Posted by Steve Klare (Member # 12) on September 23, 2017, 04:34 PM:

Paul's interference doesn't seem too bad: maybe that's what you get with a smaller motor. Mine was awful!

Posted by Brian Fretwell (Member # 4302) on September 23, 2017, 04:52 PM:

I'm just wondering how he knows it is from that motor, as when running forwards the main motor and take up motor will be running too.

Posted by Paul Adsett (Member # 25) on September 23, 2017, 05:09 PM:

Yes, both motors run all the time. I know its the front motor because it kicks up a devil of electrical noise in rewind, and in normal forward play mode if I press on the back of the motor shaft it changes the electrical noise. The level of the noise is constant and unaffected by the amplifier volume controls. Funny thing is there is no electrical noise when I connect up to the aux output sockets and into an external amp. I can only hear it when using headphones with the internal amp. It's not really bad, kind of like listening to a 78rpm record, or a dirty optical track, but magnetic tracks should be noise free and it is annoying on silent film passages.

Posted by Graham Ritchie (Member # 559) on September 23, 2017, 05:16 PM:

Paul would running an earth wire connected from the motor case to the chassis help?

Posted by Andrew Woodcock (Member # 3260) on September 23, 2017, 05:16 PM:

I don't dispute anything you're saying here Graham regarding the both motors, but then how does that work out then?

What tells the pair of motors on the arms what speed and power to rotate at and deliver and therefore what tension to apply in both forwards and reverse projection?

Load cells, potentiometer etc etc.
From my limited experience with these projectors, I didn't remember seeing those levels of sophistication.

I'd have thought a machine having individual motors for both take up and rewind duties, then when either is not required, it would be freewheeling unenergized and freewheeling only due to a one way clutch arrangement on both hubs?

Given that I'm told it is energized and running, I would think Steve will be spot on here in suggesting the brushes are towards the end of their serviceable life, minimum.

It would certainly go a long way in explaining what you're experiencing Paul.

Posted by Graham Ritchie (Member # 559) on September 23, 2017, 05:27 PM:

Good question Andrew...I cant remember how it works it been a long while since I came across this. Its interesting to note that if that fwd rewind motor stops when projecting fwd the film will become tight on that feed arm. If I remember right both motors are wired in parallel. It does seem weird, as I would have thought that there would be no current flowing to the rewind motor on fwd...but somehow it does. If you pull the back cover off and press play with no film both motors are seen running [Roll Eyes]

PS I dont think you will find the problem is so much with the brushes due so much as to wear, its that tiny commutator where most of the wear will be. However in saying that, removing the two screws that hold the motor rear cover with its brushes, and pulling it off in place will give you access to the back of the motor to clean as described above. Its very important to carefully clean out the build up of deposit between "each commutator segment" for that motor to run properly.

Posted by Andrew Woodcock (Member # 3260) on September 23, 2017, 05:33 PM:

A bizarre arrangement then Graham, if ever I saw one???

Posted by Graham Ritchie (Member # 559) on September 23, 2017, 05:46 PM:

The GS1200 is bizarre, that why owning a workshop manual for it is so important.

Posted by Andrew Woodcock (Member # 3260) on September 23, 2017, 05:53 PM:

Yes, of course.

Posted by Graham Ritchie (Member # 559) on September 23, 2017, 07:04 PM:

Just a thought Paul...can you fit a small noise suppressor onto the motor? [Smile]

Posted by Bill Parsons (Member # 244) on September 24, 2017, 12:03 PM:

Not really bizarre, although both motors turn, both spindles do not, as the gears attached to the motors have one way bearings on them.It is one of the few things simplified on the GS1200 all you have to do is change the polarity on the motors between forward and reverse and the appropriate bearing/clutch grips, it also makes it very smooth going from forward to reverse in the cue mode, much better than some other projectors, just instant light action key switches

[ September 24, 2017, 01:14 PM: Message edited by: Bill Parsons ]

Posted by Stuart Reid (Member # 1460) on September 24, 2017, 12:25 PM:

Nice to hear from you, Bill!

Posted by Andrew Woodcock (Member # 3260) on September 24, 2017, 01:24 PM:

It is simplified Bill, but in doing so it just means in one direction or another, there is always one motor running that needn't be.

It might well have been an advantageous and simplified design aspect in the earlier years after these were first made and when spares would have been ten a penny, but nowadays, it would be advantageous to just allow the spindle not needing to be driven to just simply turn by freewheeling from a separate clutch bearing attached to the hub, given that spare spindle hub motors are no longer easily found.
The motor spindle then could just remain stationary in one direction for either reel arm assembly.

Anyhow really nice to see you posting here Bill and thank you again for yet another expert explanation from your vast knowledge of these machines. [Smile]

Posted by Andrew Woodcock (Member # 3260) on September 24, 2017, 07:11 PM:

https://www.youtube.com/watch?v=C2cMG33mWVY [Wink]

Posted by Andrew Woodcock (Member # 3260) on September 25, 2017, 01:26 PM:

Comments above have now all been removed by Doug so my post here no longer made any sense nor now is it relevant.

[ September 27, 2017, 02:17 PM: Message edited by: Andrew Woodcock ]

Posted by Paul Adsett (Member # 25) on September 26, 2017, 03:47 PM:

Well the problem has been fixed, at least for now. As I said earlier, I found that the electrical noise originated from the front motor, and that the noise was sensitive to finger pressure at the back bearing of the motor. I found that I could greatly effect the volume of the noise by pushing with my finger nail on the end of the motor shaft. So I though I would try something. I held a cotton tip soaked in alcohol onto the rear bearing wile the projector was running, and the level of the noise went down by about 10db! Today, the noise is negligible and not audible when playing film.
Sometimes you just have to try something to see what happens! [Smile]

Posted by Andrew Woodcock (Member # 3260) on September 26, 2017, 04:01 PM:

Alcohol will certainly clean things up in the area Paul.
Do you think the free end bearing is in need of lubrication or perhaps is a little worn?

Posted by Paul Adsett (Member # 25) on September 26, 2017, 04:20 PM:

Quite possibly Andrew, but I don't think that's the problem. We all know how hypersensitive GS1200'S are to any form of EMI(electromagnetic interference). I swear my GS1200 will snap crackle and pop like a bowl of Rice Krispies if someone so much as switches a light on in the house. So I think the noise is probably associated with brush dirt in the motor and the alcohol penetrated the motor and bearings and somehow beneficially affected some existing internal arcing condition.

Posted by Andrew Woodcock (Member # 3260) on September 26, 2017, 04:27 PM:

It would certainly do that Paul.
As we all know from industry, keeping your machinery clean and free from contamination amounts to at least 75% of all routine maintenance ever needed! [Wink]

Posted by Terry Sills (Member # 3309) on September 26, 2017, 04:27 PM:

Things always seem to work better when one is under the affluence of incahol [Wink]

Posted by Andrew Woodcock (Member # 3260) on September 26, 2017, 04:30 PM:

Even the GS 1200 seems to like it! [Big Grin]

Especially as it is pure 100% [Wink]

Posted by Paul Adsett (Member # 25) on September 26, 2017, 04:32 PM:

Strange beasts these GS100'S, they need constant TLC to maintain their spectacular performance capability. Eumig's just mind their own business and keep chugging along! [Smile]

Posted by Andrew Woodcock (Member # 3260) on September 26, 2017, 04:33 PM:

High maintenance Paul, just like many women! Ouch ha ha. [Big Grin]

Posted by Graham Ritchie (Member # 559) on September 26, 2017, 07:31 PM:

Paul

That internal arc you mention will be down to the gummy commutator in contact with the brushes. Cleaning/scraping carefully out the build up between each segment on that commutator is very important for that motor to run properly. If you remove the two screws on the back of the motor, you can remove the rear cover with its brushes to gain access to those two brushes and most importantly the commutator itself. To put back together, use a couple of cotton buds with the ends cut off to gently compress both brushes as you slide the rear cover back on.

The motor does not need to be removed and the job can be done in a hour or so. The last time I did this was to both motors in place and never had any more problems since.

The diameter of the commutator is incredibly small and wears out badly due to the small dia of it...its real dinky toy stuff. Hopefully you still have life in the commutator and a good clean/ polish up with fine 600 wet and dry plus the doing the segments will give you a few more years out of the motor....its well worth doing. [Smile]

Posted by Paul Adsett (Member # 25) on September 26, 2017, 10:15 PM:

Thanks for that tip Graham. I will give it a try.

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