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Author Topic: Platter Drive Motor Diode Michael West Film Handler Posts: 67 From: Halifax, Nova Scotia, Canada Registered: Apr 2000 posted 02-10-2003 11:44 AM                        i have had some platter drive motors repaired on our strong international platter system (ap 3 auto programming platter), generally they just cleaned the armatures and replaced bearings and brushes, but they came back with poor results so the motor repair shop noticed they have diodes and suggested we bypass these. so my question is what are these diodes in for? the older units did not have diodes.  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 02-10-2003 12:02 PM                     Someone correct me if I am wrong, but the reason for the diodes in the Potts/Strong/CFS/ORC 'vacuum cleaner' motors is because the motors are DC-operated, and will not function on AC. Another theory that dawned on me just now is that the diode might be there to prevent the motor from becoming a 'generator', the diode would block the DC current coming from it. -Aaron  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-10-2003 02:12 PM                     DO NOT remove or bypass the diodes! The motors would be very sluggish, and will not have any torque to speak of if you did.  |  IP: Logged Michael West Film Handler Posts: 67 From: Halifax, Nova Scotia, Canada Registered: Apr 2000 posted 02-10-2003 04:08 PM                        Aaron as far as i know it is ac and Paul, we bypassed a diode on just one motor (experiment) and it has never worked better. i will refrain from any other (experiments) as i await more responses.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-10-2003 05:46 PM                     Michael, that is interesting. I have no explanaion for that. The thing I know is that if, the doide shorted out (the same as it being bypassed) the platter would grossly under-feed. Try that on payout....and see what happens. It'll probably work on take-up, but it would not surprise me that if you have a fast starting projector, the elevator might hit bottom before the inertia on the take-up platter is overcome. But since you raised my eyebrow on this, I'll proof it for you on my CFS machines in a few days. Meanwhile, I still stand firm on my orginal recommendation.  |  IP: Logged Pat Moore Master Film Handler Posts: 363 Registered: Mar 2000 posted 02-10-2003 08:48 PM                     I'm with Paul on this. The diode is required to provide a half-wave pulse to improve starting torque on that motor. I'd be really surprised if performance improved without it. Pat  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 02-10-2003 08:53 PM                        The only way that I can see removing the diode not adversely affecting operation is if the deck is timed really 'fast'.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-10-2003 09:42 PM                     Yes...and that in itself can cause some very nasty problems.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-10-2003 09:58 PM                     Also remeber that the take up and feed out speed are all based on the same variac output as a base so timing will be a mess without the diode  |  IP: Logged Michael West Film Handler Posts: 67 From: Halifax, Nova Scotia, Canada Registered: Apr 2000 posted 02-11-2003 10:40 AM                        well, it looks as if we will be removing the diodes anyways - and yes our platters timings are "all over the map", so it concerns me, i have mentioned this and was more or less ignored but at least i tried. the method used for timing platters here is to replace the drive motor prior to show and adjust as the movie plays!!! it is good to know the information you have all sent for future reference, much thanks.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-12-2003 11:06 AM                     A word of caution if you are part of a circuit before you modify anything get permision from the service engineer of your theatre  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-12-2003 01:14 PM                     Not only what Gordon said, but keep in mind you could "over-voltage" the components which could shorten the component's life, especially the electronics in the pay-out heads.  |  IP: Logged Michael West Film Handler Posts: 67 From: Halifax, Nova Scotia, Canada Registered: Apr 2000 posted 02-12-2003 04:08 PM                        Gordon i guess the projectionists in charge have told me that our theatre tech. had recommended that we do this!? Paul, the projectionists in charge told me that economy is much more important so to burn a motor out ma kes much more sense!!!!? gee, i feel so ignorant.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-12-2003 04:32 PM                     I would be concerned about the variac being damaged as the current load will be higher on ac than 1/2 wave dc  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-12-2003 04:48 PM                     Michael, if it were me, I would just flat not do it. There is absolutely nothing to gain, but the chance of damaging the equipment is very high. Gordon is correct with his assessment. Spend a buck to save 2 cents. That's what is going to happen.  |  IP: Logged

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