8mm Forum: GS1200 Speed Problem

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Posted by Robert Tucker (Member # 386) on February 19, 2007, 03:40 AM:

I need someone's help on this one. I have a problem with the speed of my GS. It seems it starts to fluctuate. I first thought, as I have not used it in a while it was down to the switches not being used for a while. So I used a bit of contact switch spray to clean the switches, which I have been told, can get tarnished if not used for a long period of time.

Well I tried this last night and it still has the same problem the speed sometimes goes up or down but not so much that it effects the picture (to flicker). So sometimes when using the variable knob on 24frps it does not actually work as the speed does not go up or down the projector does it by itself? I assume that this might need a new speed board as this is the only thing I can think of that has gone wrong with it? And if so how easy are they to fit and where do I find one?

Oh should I leave it to a professional someone like Bill Parsons?

Posted by Simon McConway (Member # 219) on February 19, 2007, 04:44 AM:

This happened to one I had back in 2004 I think. Unfortunately, it was the motor windings at fault, meaning a motor repair. You will know if it is this problem if you see excessive arcing and sparking inside the motor. Bill Parsons sorted it out; we had to send the motor away to be re-wound, at a cost of about £100. Bill refitted the motor and checked the machine over and it's been fine ever since.

Posted by Robert Tucker (Member # 386) on February 19, 2007, 05:10 AM:

Hi Simon

Thanks for that but i did take the back off as i ran the projector, so thankfully it's not the motor as i did not see any sparks flying. It sounds like you had a right nightmare! Just hope it can be easily fixed as it's my pride and joy!!!

Posted by John Clancy (Member # 49) on February 19, 2007, 05:12 AM:

Are you able to check if this happens using sync' pulse?

I sometimes have my machines doing the same thing but after a bit of use they settle down.

Posted by Kevin Faulkner (Member # 6) on February 19, 2007, 05:32 AM:

Robert,

This is the sort of Symptoms you get when the Motor Windings start to become shorted. I have seen this a few times in the past and one way to check this out is to feel the motor and see if its extremely hot (nearly burns your fingers).

If its only warm then it could be the speed control board or some diodes on the main board which have become very hot and then caused dry joints.
You can check this by removing the back and inspecting the underneath of the main circuit board. If there is a very dark patch in the centre of that board then it could be these diodes.

I'm willing to have a look at it for you if you wish.

Simon, Do you have the details of that motor winding company please as I have a GS motor which needs rewinding. I know you gave me the details way back but it was on my old PC which I no longer have.

Kev.

Posted by Robert Tucker (Member # 386) on February 19, 2007, 07:14 AM:

Hi Kevin.

Thank you for your help on this one,

If you could tell me which circuit is the main board and the best way to get to it and inspect it as i don't think it is the motor as i did have my hand on this briefly but ill check again? Assuming it is some diodes on the main board, or if it’s the speed board which I think might be the main problem. But I will check this again and let you know my findings.

Posted by Kevin Faulkner (Member # 6) on February 19, 2007, 07:21 AM:

The main circuit board is the one across the bottom (full width) of the machine. Take the rear cover off the machine and then turn the machine upside down to inspect the underneath of the board. Are you still able to select 18 & 24fps and do you get speed variation at both speeds or just 24?

Kev.

Posted by Robert Tucker (Member # 386) on February 19, 2007, 07:36 AM:

Selecting 18 & 24fps is not a problem, which I can select and normally does work. It’s just the speed variation. Sometimes I get speed variation and some times I don’t get speed variation, in other words the projector goes to it’s normal speed then slows down then speeds up by it’s self and the variation speed control then sometimes will not work?

Posted by Kevin Faulkner (Member # 6) on February 19, 2007, 08:06 AM:

Very strange. It's just the sort of thing you get when the selector switch is dirty.

While you have the back off double check the 2 connectors on the extreme RHS of the main board. The wires come from that rear board with the speed control and ESS switches. Also check the ESS switch isnt dirty.

Kev.

Posted by Simon McConway (Member # 219) on February 19, 2007, 11:02 AM:

The rewind company are: F W & P G Mason 01629 650 738. Had mine done in March 2004 at a cost of £106.93.

Posted by Robert Tucker (Member # 386) on February 19, 2007, 11:29 AM:

Kevin,

Sorry can you tell me what you mean in relation to RHS of the main board. I will have another look, but I did clean all switches inside the machine. Would it help if I undo the connectors and re connect these to see if it solves the problem?

Posted by Kevin Faulkner (Member # 6) on February 19, 2007, 11:33 AM:

Yes Robert it's worth trying. RHS (Right Hand Side).

Kev.

Posted by Robert Tucker (Member # 386) on February 20, 2007, 03:24 AM:

Well i checked over the machine last night and it seems it's the motor as it got hot after me running it for 20 mins. I assume a new Elmo motor is out of the question?

Posted by Kevin Faulkner (Member # 6) on February 20, 2007, 04:13 AM:

Robert, Was the motor extremely hot? Wittners have them on their website. They are very expensive though.

Wittner Kinotechnik

Think it would be cheaper to have your original rewound by the company Simon used. (details above)

Kev.

Posted by Robert Tucker (Member # 386) on February 20, 2007, 07:30 AM:

Kev, it was hot to touch after 20mins of running compared to the other motors meaning the fan motor. From memory I would have a slight slow down in speed and then it would go back to the original set speed this would happen when running a 1200ft reel towards the end of the reel, or a 600ft reel, which was not such a problem until now. Since then it has got allot worse. No sparks to report coming from the main motor, but I did change over the black screws either side of the motor and the flints with the springs? I did notice that one was shorter then the other?

I just wonder why this motor has the only flaw; I gather this is because it is the main motor of the projector.

My last question is how easy is it to fix or should I say fit yourself?

Posted by Barry Johnson (Member # 84) on February 20, 2007, 01:19 PM:

Hot (very) motor casings can also be attributed to a start up capacitor that is life expired.It will also give rise to variable running speed.
I have already informed another member of this on this website as he too has a similar problem.

Posted by Kevin Faulkner (Member # 6) on February 20, 2007, 04:10 PM:

Barry, The GS uses a small DC motor so it doesn't use a start-up capacitor. These are only used on AC synchronous motors such as most 16mm machines and the ST1200.

A very hot motor casing on the GS motor very often points to the windings shorting. Due to the current drawn and the fact that the motor is running slower results in the speed control board trying to turn the wick up to maintain speed which is why you end up with having no adjustment with the +- speed control. If it gets so bad you can even loose the ability for it to run at 24fps.

I have got a motor here at the moment which exhibited exactly those faults. With the shorted windings you get speed variations due to the intermittent shorting and at the same time the motor runs very hot.

In this case the guy got my last new motor which of course cured the problems and all was restored to normal running.

Kev.

Posted by Barry Johnson (Member # 84) on February 21, 2007, 01:35 PM:

Thanks Kev,I stand corrected.
Barry

Posted by Kevin Faulkner (Member # 6) on February 22, 2007, 03:55 AM:

Your welcome [Smile]

I just wish it was that simple [Frown]

Kev.

Posted by Lee Mannering (Member # 728) on February 22, 2007, 04:07 AM:

Is this motor any good on ebay?

Item number: 230095410052

Posted by Kevin Faulkner (Member # 6) on February 22, 2007, 07:42 AM:

Lee, That will be no good as it doesn't have the speed control sensors built in.

BTW what voltage is that motor?

Kev.

Posted by Rick Skowronek (Member # 385) on February 22, 2007, 04:03 PM:

Hi Everyone,

Couldn't help but just put my 2 pence in. There is no way I wish to pass any knowledge of GS1200s or to even remotely possessing the knowledge of Kev or any of the other long term GS owners. I do have, however, many years in the electronics engineering realm and just want to offer one more possibility before 100 pounds is spent on a motor rewind (not that it may well be necessary). As kevin mentioned, it makes real sense to check the motor rectifier diodes on the board to insure they haven't started going bonkers. If they do, the actuaql DC voltage available to the motor and it's regulator, may be insufficient to always hold the voltage high enough to power it. Second, and it certainly is a consideraion, is the output regulator transistor, or even one of the earlier circuit components, for the motor.

One certainly has to remember the age of these beasts and also realize they were somewhat in the early days of solid state technology. I have worked on literally hundreds of various machines and back in that day semiconductors would degrade eventually and lose many of the characteristics that make them function. Usually, but not always, they just up and fail so the bad component is easy to find. Other times, though, heat is the worst enemy. At times the device works just fine when starting up but then goes bonkers when it starts it's normal use heatup.

Anyway, just a suggestion to eliminate the possibilities before embarking on expensive solutions before eliminating the less expensive (possibly tougher to find, though) other ones. By the way, sometimes the best test for this is a spray product called Circuit Cool or something similar in the UK. It is a spary coolant you can spray directly on components to instantly cool them down to see if it does go back to normal operation while it stays cool.

Good luck and you definitely have the best of the best on the case.

Rick

Posted by Kevin Faulkner (Member # 6) on February 22, 2007, 04:21 PM:

Uummmm this is now getting difficult to describe. The diodes in question are in fact 3 in series which go for arguments sake between the motor and ground. The voltage drop accross these 3 is used as means of the logic circuit knowing the motor is running. Hope that makes sense?
The fact that these 3 dioes are in the neg to ground circuit of the motor means that they are subject to quite a bit of stress and vcan overheat and cause dry joints. I think the fact that Robert says the problem is worse in forward than reverse probaly counts these out.
The few times I have found a motor on its last legs has caused very strange results indeed. I have found that the motors work reasonably well in reverse but not in forward but the main thing is that they run extremely hot, nearly too hot to handle.
This running reasonably well in reverse I suspect is to do with the voltage polarity. I do know that in these cases a replacement has cured all the problems.

If Robert were able to get his machine over to me I could try my motor in his machine and we would then know for certain.

Robert, how about it?

Kev.

Posted by Robert Tucker (Member # 386) on February 28, 2007, 04:05 PM:

Hi Kev,

Sorry I was away and just got back and read your reply, to answer your questions, it is the same in forward or reverse to be honest. I have also noticed something on the motor which is a green Ceramic Disc Capacitor, do you know what this is for and if so will it cause the motor to misbehave?

I am happy to get the machine over to you but I have one big problem I have moved to the out skirts of Kent in Barnhurst. Plus I don’t drive. As I know you will be able to solve the problem have you any suggestions on how I could get this over to you safely?

It is so strange as if the motor was running at correct speed I would have my GS back as normal. I have never had a problem with it full stop and has been very kind to my film collection over the years. Unless I can get this fixed I will have to postpone my programme at Bristol Film festival.

I do have a super 8 beaulieau projector but as you can understand it’s not in the same league as a GS. I have also tried to find the very rare Fumeo Super 8 500w Xenon pedestal projector but they are so hard to find as a professional machine that will show feature length long movies on the road.

Posted by Joerg Niggemann (Member # 611) on February 28, 2007, 05:48 PM:

Just some thoughts:

If the problem only occurs in forward mode, I can't imagine that there's a problem with the speed regulation circuit, as it always works the same way in both directions.

To check the motor in this case, we could change the motor's supply voltage polarity and check if the fault still only appears in forward mode (the motor now turns backward). If yes, the motor should be ok. Of course, we didn't thread a film during the test [Wink]

.

Now the last thing to check if we found the motor being ok are the motor direction switch contacts (2 relays)...

As I said - just thoughts!

Joerg

Posted by Kevin Faulkner (Member # 6) on February 28, 2007, 06:05 PM:

Robert, If it's in both directions it really does sound like the motor.

I'm a motor bike rider so I cant offer to fetch it for you.

What you could do is send me just the motor and I can check it out for you and then ship it back. Should only take a few days in total. That would save having to ship the whole machine anywhere. I work up in London so if you also work in London we could meet up so I could pick the motor up from you.

The motor can be removed very easily by removing the four screws in the plate which secures it to the machine case. Also remove the plugs from the main board.

The green capacitor is in fact a thermistor for removing spiky interference that the motor generates when running. If this is not present you can hear motor noises through the amplifier.

Hope that helps, Kev.

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