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Author
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Topic: Strong AP3 Platter Speed
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Bernie Anderson Jr
Master Film Handler
Posts: 435
From: Woodbridge, New Jersey
Registered: Apr 2000
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posted 06-10-2008 10:25 PM
I have AP3s in a theatre that I maintain. I'm not used to these particular platters, I grew up on the Potts version, which was very simple in design. What has started to happen over the past couple of weeks, is the payout seems to have slowed up and is now starting to wrap the film around the brain. Over the weekend , it was reported that it wrapped so bad that someone had to be there to spin it by hand. These platter are 8 years old, and really never have given me any trouble up til now. In reading the manual, the timing is very similar to the earlier pots platters. But even after timing them, I'm still getting a weird wrap. Now I notice the control board in the brain and the manual says not to touch anything in there, could there be some trouble with the LED or the board in there. More specifics, changing the brains between decks change nothing and the belts are looking a little worn, some have some cracks in it. After adjusting the motor to where the platter at least feeds to a certain degree, if you spin the deck by hand, it almost feels like there is no motor engaged. I remember with the older Potts platters, the belts were always a problem. Could a belt throw off the timing on the platter that much? Any thoughts?
Thanks
Bernie
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Monte L Fullmer
Film God
Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004
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posted 06-11-2008 04:33 AM
how's the brushes in those AMTEK/LAMB vacuum platter motors? I bet you're coming up due for some brush replacements.
Phase control brains - the LED's do get tired in them and will affect your speed some, let alone the voltage coming out of the wall could have some variances as well. And phase control brains, along with them vacuum motors are very sensitive to voltage fluctuation in a very small amount.
A lot of folks do a phase control to microswitch exchange on the brains to eliminate such variances, but the tradeoff to microswitch is the removal of the continuous film payout to an 'off/on' power situation which the platter is either "off", or "on" form of operation.
Personally, I've never like the "on/off" status of the STRONG platters -from POTTS to the newest AP3's using microswitch brains for this simple reason of the lack of continuous payout.
(You might say, I'm rather spoiled by the payouts of the AW3, LP-270's and other makes that handles film on a continous flow).
For, if that film is laying on a deck that isn't centered, but eccentric, a microswitch controlled platter can easilly throw that print due to the 'on/off' status.
..my .02's worth -Monte
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Dave Macaulay
Film God
Posts: 2321
From: Toronto, Canada
Registered: Apr 2001
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posted 06-11-2008 11:05 PM
Do a quick test. Install the payout and set the tension roller unit holding pin in the lowest hole. Disconnect the drive motor using the lever (mechanically, not electrically). Pull the payout arm to full ON. Now pull down the AP switch roller for that deck while the arm is still at full ON. The motor must slow down a bit when switched to rewind for the payout to work properly. I expect that with your payout control the rewind speed will be higher... ie the rpm will audibly increase when you pull down the AP switch roller.
The platter design requires that the payout platter be capable of going slightly faster than the rewind platter. The Alpha/AP design uses a series resistor in rewind mode plus the drag of the takeup film tension to guarantee this speed advantage. Timing the platters just ensures that the platters turn at roughly the same speed for a given motor voltage. Using microswitch payouts also guarantees the speed advantage assuming timing is correct... but the phase control payout CAN (and should) give smoother operation with less speed hunting.
Adjustment: Open the phase control box: remove the tiny screw and washer and gently wiggle and lift the cover off. The arm must be fully OFF or the little plastic shutter thing will jam in the cover slot and pull up/off. That's not serious but the way it goes back on and how the spring works are not entirely obvious if you have one in pieces.
Check that the basic adjustment is good: the plastic shutter has a little rounded notch in it, this should align with the sensor lens (lower pcb) when the arm is fully ON. This is adjusted by loosening the two screws attaching the control box to the payout plate, the box pivots on the flat head screw and is locked in place by the round head screw. If both are just finger tight the control box can be turned to set the shutter adjustment. The LED should be roughly centred above the sensor but a bit off to the side away from the shutter, you can move the upper PCB and/or bend the LED wires to adjust.
Now the trimpot adjustment. You need to have a powered platter in a reaonably dark place. Luckily most platters are in projection rooms... almost always easy to get reasonably dark. Get a flashlight and a trimpot tweeker (or tiny flat screwdriver).
Install the payout on a deck you can reach it on. Lock the tension roller unit holding pin in the lowest hole. Disconnect the drive motor, again using the lever (mechanically, not electrically).
Find the trimpot and get your tweeker/driver in its slot using the flashlight then turn the light off - stray light will really affect the adjustment and you will notice the motor runs if light shines into the sensor lens. Pull the arm to full on. The motor should run and you should see some sign of LED light. Now adjust the trimpot for just above maximum speed: this means turn it down (CCW) until the motor slows down noticeably. Now turn it up (CW) very slowly until the motor reaches the highest speed attainable... then turn it higher a fraction of a turn more. You should notice the LED is brighter than before you touched the adjustment.
This adjustment isn't described in Strong literature as far as I know, nor have I seen a schematic for the phase control payout. The trimpot might be to avoid some catastrophic failure mode and adjustment suicidal... but I think it just compensates for aging LEDs and I've adjusted several - this is my normal fix when an otherwise fine Alpha/AP platter starts doing brain wraps for no good reason.
This is reasonably safe, but has some risk. There's AC power on the payout PCB and wires - this should be only the variac voltage, maybe 50 volts or so with the holding pin engaged. The variac is not an isolating transformer, though: if the power cord/plug are miswired there may be full line voltage present. Be careful.
DC platters are totally different, don't try this crap with them (DMC or SCDC).
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