This is topic Drive Belt Issue With Elmo ST-1200HD in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:;f=1;t=008170

Posted by Roger Shunk (Member # 2836) on May 13, 2013, 05:47 PM:
Hello everyone,

I have two Elmo ST-1200HD's. My primary one I use here at home and the other one is my traveling companion I use to show movies

I just put all new belts on my traveling HD and tested and everything was fine. It sat in cool storage for a couple months and I took it out Sunday to show some films and it made a funny noise coming from the top inside of the projector. I popped the back cover and the top drive belt was slipping when the film is running but not slipping when you run it without a film? When the film runs the bottom of the belt is tight but the top of the belt is loose and flopping around. It's a brand new belt so has anyone experienced anything like this before? It does not seem like the belt is stretched out since it's brand new and no use on it until yesterday.
Any information on the subject would be greatly appreciated!
Thank you,
Roger Out
Posted by Joe Taffis (Member # 4) on May 14, 2013, 08:17 AM:
Roger, it sure sounds like you have the wrong belt on there....
Posted by frank arnstein (Member # 330) on May 14, 2013, 09:27 AM:
Hi Roger,

You probably do have the right belt there and you don't want to use a loose belt.

There is an important friction clutch in the take-up spindle drive system. It allows the top driving belt to run constantly at a set speed while the driven take up reel slows down or even stops turning.
The belts tension and speed should be constant and if there is an increase in load, like the take up reel being manually held by hand or the reel getting very full and heavy, then the friction clutch will start to slip, continuing drive but limiting torque to the spindle.
Thus the belt keeps driving the spindle with the same torque regardless of the output speed. The fuller the reel gets, the more slip will be occuring at the clutch.

If your friction clutch is set too tight and can't slip early enough, then the driving belt will start to stretch, trying to slip and it bundles up on one side as yours is doing. Its trying to work too hard and needs relief from the friction clutch by it slipping.

The answer is to ensure the friction clutch starts slipping whenever you slow down the take up reel with your fingers and force it to stop turning. Instead of the top belt bunching up, it should stay even and keep rotating even when the take up spindle is momentarily stopped by hand. As soon as you let the spindle go and it resumes turning, the friction clutch will then stop slipping as it is no longer under load.
The belt should keep going around at the same speed regardless of the torque load from the spindle. This driving torque is controlled and limited by the friction clutch and so it must be set to allow slippage to occur at the right load.

Look at your clutch to see if its working. Test it and see what you find... then let us know. This clutch and belt are very important for correct operation of all ST-1200's and many other Elmo ST models with the same clutch set up.

Good Luck on it.

dogtor frankarnstein
[Wink] [Smile]
Posted by Vidar Olavesen (Member # 3354) on May 14, 2013, 10:08 AM:
Super info, just the same problem I have on my machine. Will send it to Mr. Parson for a cleaning, lubing and greasing. Will ask him to check this too, cause it is same symptoms I have
Posted by Joe Taffis (Member # 4) on May 14, 2013, 10:40 AM:
Roger, I thought you were referring to the top motor drive belt, not the long take-up one on top. sorry
Posted by Roger Shunk (Member # 2836) on May 14, 2013, 12:02 PM:
Greetings everyone,

Frank I sent you a PM

Thanks Dr. Frank for your excellent diagnosis of the patient. I had sent the unit to Leon Norris for a complete overhaul and he
put on all new belts,lubed and made any necessary adjustments. When I got it back from him I tested everything and everything worked like it should, and I then boxed it up and put in storage since this is my back-up projector. So I don't know what happened here just sitting in storage?

I will check out what you have told me to do and let you know what I find out!
Thanks again for your help!

[ May 14, 2013, 01:56 PM: Message edited by: Roger Shunk ]
Posted by Joe Balitzki (Member # 438) on May 14, 2013, 04:21 PM:
Roger your Private Mailbox is Full; please empty it so I can send you a PM. Thanks!
Posted by Roger Shunk (Member # 2836) on May 14, 2013, 05:44 PM:
deleted my messages go ahead and send me your PM

Visit for free equipment manual downloads. Copyright 2003-2019 Film-Tech Cinema Systems LLC

Powered by Infopop Corporation