Film-Tech Forum ARCHIVE: LP 270 timing problems

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Posted by David Favel (Member # 1125) on 01-22-2003, 01:18 AM:

My LP 270 is playing up on 1 deck only.
Every now & then the brain would advance the payout motor then when it was due to stop, it just kept going.
I thought it was a small adjustment, so checked the magnet thingy with the swing arm. O.K.
Started Two Towers tonite & the thing kept spinning till I yanked the magnet arm.
Solutions?

Posted by Paul G. Thompson (Member # 655) on 01-22-2003, 01:26 AM:

It has been years since I worked on one of them, but it it uses reed switches the chances are it is stuck because of pitted/arced contacts. The magnetic reed switch (if that is what is used) needs to be replaced.

Posted by David Favel (Member # 1125) on 01-22-2003, 02:13 AM:

Thank you oh great one!

I humbly bow & name myself not worthy.

Will try tomorrow & advise

Cheers

Posted by Gordon McLeod (Member # 33) on 01-22-2003, 09:17 AM:

Also check the SCR's to make sure they haven't opened circuited

Posted by Darryl Spicer (Member # 711) on 01-22-2003, 09:26 AM:

Check to make sure that nothing is preventing the arm from swinging all the way back. I have had that happen before. I have also had to replace the whole card do to this problem.

Posted by Bill Langfield (Member # 818) on 01-22-2003, 12:54 PM:

Hey David,

I would suggest the 'magnet thingy' is not lined up correctly with the payout arm.

Each plate/deck has it's own set of FET's (Field Effect Transistors) even if the brain/payout seems set correctly and works fine on all other decks if a magnet is not set correctly on a deck it will cause lag or payout too fast. (I'm not too sure which of these wrap-around conditions I hate worse)

All I do I is get someone to hold the brain down, with the pay-out arm at stop postion, and 'force' the magnet towards the 'stop' FET until the motor stops, then let it go and see what it does, if not right, 'fine' tune it again. (this can be done while on screen, hence the need for help - to get them to keep an eye out that the wrap-around is not getting too bad, and that the brain tends to want to lift out when forcing the postion of the magnet)

I could be talking total rubbish, but I've been through this many times with Specos. You are talking about a Speco LP-270 right! ??

BTW: I'm sure the problem is created by a sticky join going through, and slamming the payout arm to stop then to full speed, there-by knocking the magnet out of position.

PS Speco's are a dream compared to CNR's or Christies so dont be put off.

Bill.

Posted by Gordon McLeod (Member # 33) on 01-22-2003, 03:13 PM:

If this is the famous red column white deck Specco then I have yet to see one with fets in it. The ones up here use 2 magnetic reed switchs to gate to SCRs on depending on the speed requirement

Posted by Bill Langfield (Member # 818) on 01-22-2003, 03:32 PM:

Gordon,

Surely, reed switching would make the pay-out switch back and forth like mad.

Without seing how the platter you are talking about is set-up that just sounds 'wrong'

However I've been wrong many times before.

I'm just trying to explain to David what I work with, hopefull it will help.

Bill.

Posted by Gordon McLeod (Member # 33) on 01-22-2003, 03:43 PM:

The magnet attached to the control arm moves back and forth switching either reed switch on or off in such turning the SCR on or off(since it is feed ac it drops at the end of the 1/2 cycle with no gate present) That allows effectively 2 speeds

Posted by Bill Langfield (Member # 818) on 01-22-2003, 03:49 PM:

Gordon,

Now I think about it, your proberly CORRECT!
(I'm going to re-read the manual, and take another look at the wiring/circuit diagram AND the platters)

Your 2 Speed thing does apply when then the take up is not activated, however after that has been actvated, the hall effect of the FET's take over.

Look, I didn't even know what the break-down button did!!!, so I'm clueless

But it all depends where the the magnet is in regards to the reed switch and pay-out arm postion, that is his main problem, regardless of how the electronics work.

If his platter keeps spinning in pay-out not matter how close he moves the magnet to the FET/Reed switch stop, then there IS a problem.

As I said the magnet can be thown by a sticky join.

Bill.

Gezz Brad Kick me off, OH no don't please. Can't believe I talking crap again !!!! Trying to be smarter than I am. Ouch.

Posted by Gordon McLeod (Member # 33) on 01-22-2003, 06:34 PM:

acording to the book i have there is no */@#ing fets in that mule just 2 SCR's controlled by 2 reed switchs
If it keeps spinning it could be a shorted SCR or reed switch

Posted by Darryl Spicer (Member # 711) on 01-23-2003, 11:07 AM:

This is my experience that I have witnessed with these platter systems over the course of ten years working with them. If you just run the platter as a payout no take up like you would when running an interlock set up. The platter runns in an on off senerio. No reel speed control just on and off and the speed is determined by how long it stays in the on position. Now when running it in the normal set up payout and take up both working. the payout runs more smoother. If you ever noticed when running the platters and the controle arm does not swing all the way back to the stop point the payout platter will keep turning. As soon as the takeup acumulator drops the payout platter will stop spinning. So somewhere up in the box there must be a change in how power is supplied to the controle cards. As far as if it's got this or that on the boards I don't know. THis is just the actions I have seen these platters do.

Posted by David Favel (Member # 1125) on 01-23-2003, 06:00 PM:

I swapped a control card from the top deck to the middle deck (that was playing up)
I now have no problems with that deck. The card is in the shop being checked.

Posted by Adam Martin (Member # 641) on 01-23-2003, 08:29 PM:

Yes, Darryl, there is a threading mode and a payout mode on the 270. That's why you have to run the film through the variac on the payout platter (or otherwise hold it in above the two switches at the bottom of the variac) when running an interlock where you don't takeup on the same platter system. The variac should also be up when timing the decks for payout.

Posted by Brad Miller (Member # 2) on 01-23-2003, 09:07 PM:

Darryl, put in super simple mode, the LP-270 feed arm has 3 positions. OFF - SPEED OF TAKEUP PLATTER - FULL ON. When you are not using that platter for takeup, you are getting OFF or FULL ON. I usually use a 1 inch office binder clip clamped to the elevator shaft about a foot or so up from bottom to provide a medium speed when doing an interlock with these platters.

Posted by Randy Stankey (Member # 64) on 01-23-2003, 09:39 PM:

If I might add...
One thing you have to watch out with Speco platters is dirt getting down into the bearing/shaft that supports the payout magnet. (AKA: "Magnet thingy".)

Carefully pull the take arm off the shaft, then take the brain off and look down into the top of the arm where the plastic shaft goes. There's a white plastic bearing. Use a paint brush to clean all the gunk out of there and see if that helps. If not, try some stronger measures: Disassemble again and remove that bearing completely. Dunk it in a mild cleaner like alcohol or Windex or something. Carefully clean all the crud out with a toothbrush or some suitable tool. You shouldn't have to lubricate it but if you think it needs some, use 3-in-1 oil, NOT WD-40. Put it all back together again and test it. Your payout arm should move freely with virtually NO friction.

The payout arm needs to move right along with the film for the Speco platter to work correctly, If there's ANY drag in that bearing/payout arm you can cause problems similar to those you describe.

While you are at it, check to see if the plastic payout arm is rubbing against the metal plate of the brain. That's another common thing I used to find. Just pull it up/off the shaft a fraction of an inch so that it doesn't rub but not so high that it makes the film have to go over a "hump".

I would check this stuff before going into the wires and junk.
You know my motto... Check the easy stuff first! [Big Grin]