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Author Topic: AP-3 Revisited Paul Stevens Film Handler Posts: 42 From: Galena, Ohio, USA Registered: Oct 2006 posted 11-17-2006 09:53 PM                     After looking over a similar posting on this subject I wanted to inject a few comments along with the following problem with my AP-3's. Random and intermittent brain wraps seem to be our affliction. The temporary fix for this was mentioned in the earlier posts. Engaging the unused platters caster switch causes the malfunctioning platter to operate normally. Of course we have a free running platter motor, but that can be dealt with. What I set out of do, was find out why using this "Band-Aid fix", was effective in making the malfunctioning platter operate normally. After studying the schematic with the aid of Adobe Photoshop copy and repast, I was able to create three operational scenario's for comparison with the caster switch in the various configurations. After fixing an error on the original schematic, I was able to understand better just what was happening. When the unused platter's caster switch was lifted, the drive motor for that platter starts up as expected. In addition, the brain for the same platter is also disconnected from the Variac output buss now supplying power directly to its platter motor. This gives rise to two possibilities. An intermittently malfunctioning brain loads down the output of the Variac effecting everything it supplies power to without burning up. Or the Variac itself is not supplying adequate current to all attached devices. I am beginning to think that AP designed its digital line platter systems for this reason. I am going to open up the case for the Variac on one tower to see how much carbon if any has built up on the contactor wiper. This thing having to provide variable AC to so much stuff may have built up some current limiting layer that can be burnished off. Any thoughts on this would be welcome. Paul Stevens  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-18-2006 09:33 AM                     AP-3 rules I go by..... 1. Replace all Microswotches at least every three years to ensure trouble free operation 2. If an intermittent problem persists look for a broken wiper in the variac. Mark  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 11-18-2006 12:12 PM                        Mark has very good advice. To add to it: the wiper on the variac you REALLY want to check is not the obvious carbon one, but the spring steel & copper one located under the wheel "inside." Your problem is likely to be the microswitch variety or a possible loose connection inside the offending arm. (Molex plugs inside.) Louis  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-18-2006 01:51 PM                     ....I'll chime on this one as well... Check motor brushes and replace if necessary. (and PLEASE, don't lean on the decks too hard. Warped decks really mess up the payout/rewind procedure since everything depends on that one variac located in the base of the tower..) ...and look into a wrap detector from STRONG. -Monte  |  IP: Logged Paul Stevens Film Handler Posts: 42 From: Galena, Ohio, USA Registered: Oct 2006 posted 11-19-2006 12:10 PM                     Thanks for all the comments about the subject. I will take all of them into practice when the repairs actually begin. When I opened the case to take a closer look last night, I noticed the large carbon buildup in the area's I expected. Because I wanted to figure out why that "Band-Aid Fix", allowed that sluggish playout platter come back to life, I wanted to test my theory out. With two of the platters configured for a normal play/rewind operation, I lifted the unused feed caster switch to engage the motor for that platter. This is what I observed: The added platter motor electrical load to the Variac momentarily slowed the other two platters causing the film tension to slacken. The elevator lowered about three inches, than rose about one inch to compensate. The new position of the elevator, and thus the new position of Variac wiper tends to support my restricted current theory. Carbon is thickest where the wiper spends most of its time. When the contactor moved to an area of better conduction, everything started to operate more robustly. My task now is to figure out the best way to service seventeen of these things in an efficient way. Getting the carbon deposits off will be challenging without further surface damage to the Variac windings. Lots of the old reliable chemicals for cutting this stuff loose may no longer be available. Gum or pencil eraser's have worked very well in the past with thin film module contacts or card rack circuit boards. Any suggestions here would be welcome. Paul Stevens [ 11-19-2006, 06:38 PM: Message edited by: Paul Stevens ]  |  IP: Logged Tristan Lane Master Film Handler Posts: 444 From: Nampa, Idaho Registered: Feb 2002 posted 11-19-2006 01:59 PM                     To me it sounds like the problem lies more in the brush wiper than in the winding surface of the transformer. It's not uncommon for a worn brush to cause the problem you describe. Either the inner spring-wiper that Louis mentioned is getting worn out, or the carbon brush has worn down to the point where there isn't enough length left on the brush to make a reliable contact to the windings in that section of the powerstat. I would first try replacing the brush and see if opertaion is normal. You should also check "zero" voltage to make sure that the variac is calibrated properly. I believe you want 25 volts when the accumulator is in it's center postion with the threading pin engaged. I've seen heavy buildup on 20+ year old staco transformers that was easily removed with some 800 grit paper and then polished to remove any rough surface. I've never used chemicals due to the fear that it might hurt the varnish on the windings. I have yet to see the condition on any Powerstat transformers, but I have seen plenty of brush failures. Depending on the age of your platter, it will either have a Staco 1010, or a Powerstat 116CU transformer. If carbon buildup is your problem, then there's no fast way to fix it. The best way to clean the windings is to remove it from the housing. Then remove the rotor/spindle assembly so you can have clear access to the contact surface of the windings. Don't use any heavy grit paper or emery cloth or you will experience premature brush failure due to the rough surface.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-19-2006 10:31 PM                     A cuetip swab and 99% alchol is a good cleaner on variacs  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 11-19-2006 11:16 PM                     Gord is right, the q-tip and alcohol cleans them quite well. If the brush still has the narrower tip visible then it's not worn out, if the tip is gone you need a new brush. The inner brushes can be renovated if not too burned (either the ring or brush) but the parts are available if really bad. The worst part is getting the blasted variac out of the blasted box. The key is to remove the shaft: you undo 2 allen screws at the brush end and the shaft slides out leaving the rest intact, a circlip holds the brush plate assembly in. It's easiest if you pull the whole power supply box off, but after a few you can do it on the floor without too much trouble. You should buy one replacement variac if you really need to service them, removing and replacing the variac takes quite a while and if you have a good one you can then work on the removed one at your leisure. The coil assembly is most of the coat of a variac. Unless the contact area is badly burned you can dress it with fine wet/dry paper and get a good usable surface. The problem with platter PS variacs is that only about 1/2" of contact ring is used all the time and once it gets burned/pitted beyond repair you're in for a new one.  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 11-20-2006 12:17 PM                        Altenator/Motor cleaner from your local autoparts store does wonders at washing out similar carbon deposits in motors and such. I've used it on a few platter motors with wonderful results. Maybe it'll do good for your variacs.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-20-2006 09:01 PM                     Be aware that you don't want to use any solvent that leaves a conductive residue  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 11-20-2006 11:38 PM                        Correct, but being that this particular stuff is designed to be used in eletric devices, I would expect that it wouldn't leave a conductive residue, if any at all. It is simply designed to wash out carbon in motors, specifically from dust produced by the brushes, but also the carbon produced in arcing in the commutator. I belive variacs wiper assy, would relate to a commutater and brushes. Just my thoughts, though I haven't tried using it to clean out a variac myself, yet.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-21-2006 09:00 AM                     Just to make it known that ALL of the variac parts are available through us seperately. No need to buy the entire unit. Mark  |  IP: Logged

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