Century C - ghosting top & bottom of picture

[Jacob Tutt]

This might be related in some way to the topic Ryan started with his JJ. Looking for advice

In our changeover booth, one of our projectors produces a slight ghosting at the top and bottom of the image. Turning the shutter knob in one direction can reduce the symptoms on one side, but worsen ghosting on the opposite side of the frame. I've also noticed this projector occasionally produce a bit of a knock sound like the one describe by Ryan in the other thread. Only with film running, and always with dirtier or older film. I checked the vert. shaft and there was a bit of movement up and down that I was able to remove by threading down the collar at the top of the shaft. Still the ghosting top & bottom persists.

The ghosting also seems to pulse consistently somewhere between 2 to 3 'pulses' per second. With each pulse the white streaks from the ghosting are accentuated

It sounds like it could be a worn out part. Where is the best place to start with troubleshooting, or part replacements?
We have a few parts projectors here that I can try swapping components and parts with

[Mark Gulbrandsen]

Do both projectors have the same shutter in them? If this one has a drive in shutter that would cause ghosting, especially on white titles on a dark background. And, if the projector mechanism isn't making strange sounds, and the shutter is correct, then It may be a bad diode in that projectors rectifier, assuming it's not a switching type rectifier. A bad diode will cause a consistent fast pulsating like you describe. The pulsing caused by a bad diode can usually be seen just by passing light with the projector stopped, but the shutter open. Just do brief passes of light with it not running so you don't damage or crack a lens element. A few seconds at best. If the projector was fine one day, but doing this the next day, then it's probably a diode.

[Jacob Tutt]

Both projectors are single shutter with 90° blades. We have Xenex I lamphouses with Strong rectifiers. I suppose if it were a component in the rectifier, I could test by swapping the whole rectifier to the other machine?

Could a bouncing fire shutter produce this affect? On this machine the fire shutter dips a few millimetres into the cone of light, but I don't think it is enough to obstruct any light that is reaching the frame.

[Steve Guttag]

How confident are you in the 90-degree part? Have you measured it? 90-degree and 84-degree look VERY similar and a Century will ghost with less than a 90-degree shutter. You might improve things by taking out the gear lash on the GR-207 where the shutter gears mate up (and make sure all of the gear screws are snugged so the gears are not slipping). But I'd start with the shutter itself.

[John Eickhof]

two things, first check the working distance from reflector to film plane, and the size of the light spot in the heat shield on the gate between the projectors, even with a 90 degree shutter lamps like the early xenex produce a larger spot under less angle and if set to improper working distance will tend to bleed around the shutter, if working distance is good then loosen hub and move shutter slightly forward towards screen, make sdyre it clears the housing! then try it, also the GR-207 probably is worn and should be replaced, possibly the steel shutter gear too and proper backlash should be adjusted. lastly, see how much slop is in the gear train by holding the intermittent flywheel and turn the shutter blade back and forth to see how much slop is there, century heads are notorious for 5-8 degrees slop and the blade will 'float' if so gear lash adjustments need to be made as the shutter is drifting...

[Mark Gulbrandsen]

It's a good lamp house but it has a glass reflector that is likely NLA. So be careful in there. The Xenex 2 has a metal reflector. Swapping entire rectifiers is a waste of time. With the breakers off! And still having checked with a meter to be sure the power is REALLY OFF, then check each diode with your ohm meter set on the diode position. One is going to be open if this is actually the problem. You could have also dropped a phase, but the lamp would likely be noticeably difficult to light. Certain Strong rectifiers are famous for diode failures... Pictures may also help, as would it to know if this is single or three phase system.

[Jacob Tutt]

I'm sure these are 90° blades. How would I take out the gear lash on the GR-207 shutter mating gears specifically? I will check that all gears are snugged down. What is the best procedure for ensuring proper gear lash for all the gears?

Lamphouse working distance is 24" measured from the aperture to the front edge of the reflector, as in the manual, so that appears fine

The shutter blade is clamped to the shutter shaft with two flat head screws, and there is a small groove in the shaft with a pressure clamp that appears to set the fore-aft position of the shutter blades on the shaft. I would have to remove that 'clamp' to move the shutter towards the aperture. Correct?

There is definitely some slop in here, I would guess about 5° as you say John. It looks about the same amount of slop as on the projector with no ghosting issues, though
I've noticed the contact points on the gears will get a bit light orange in colour when the projectors are running, almost looks like there is not enough grease. But then when I look at them now the grease looks to have migrated back and the gear contact points are a uniform dark red colour and shiny.

I've attached some pictures here in case it helps.

Stumped... Throwing a bunch at you to see what comes back!

Shutter blade.jpg Gear Side.jpg Shutter Gears.jpg

[Steve Guttag]

The shutter bracket, where it attaches to the rear of the projector frame is only pinned on one side, if you loosen the four screws, you can pivot the bracket and take out the gear lash. Note, you don't want zero, that will just eat the gear but you want to be minimal...just a hint to slop and let your ears guide you. When the machine is on, you the gears shouldn't sound like they are grinding.

Another thing to look for is if the shutter shaft is moving fore/aft while it is running (with film). All problems show up in the shutter shaft as it is the fastest spinning thing in the projector. You can have slop in the intermittent drive gear (the one that rides up/down the vertical shaft as it is adjusted for shutter timing)...that too can introduce slop that will cause a shutter to bounce excessively. A strobe can be an aid in finding something that is not running smoothly (and will show you just how unstead most shutters are).

I would still measure the shutter. It is easy enough.

[Jacob Tutt]

Steve, thanks for the tip! I did not know the shutter bracket could pivot. Pivoting the bracket as far inboard as it will go and still there is slop in the gear train while holding the intermittent flywheel stationary. Is this a sign the gear is worn? The way you describe it sounds as if pivoting the bracket all the way inboard would take away all slop.

I've tested to see if there is for/aft movement with the projector running with film by bracing my hand against the shutter casing and holding my thumbnail to the end of the shutter shaft on the shutter side of the projector. There's definitely no drastic bounce, and if there is any it's imperceptible to me.

How do I measure the shutter?

[Mark Gulbrandsen]

Jacob,

You should have lubrication clearance that's equivalent to about the thickness of a sheet of printer paper between each gear pair This is according to Norm at Wolk, which used to make the gears, but is also long gone.. Originally, Century originally specified oil on the gears, then later, after WW-2, the Century Grease became the choice because it was thick enough that it actually stayed on the gears. Today, Super Lube is the best thing to use on them. It's synthetic, doesn't dry up or thicken over time and stays on the gears. Some people say to use Vaseline, but it's much thinner, and it's lubrication properties are actually poor, and it dries up. If you google Vaseline as a lubricant you will see countless links saying "DON'T USE IT AS A LUBRICANT" In the sound head gear box I use Mobil SAE 80W-90 synthetic gear lube. Projectors that I used the synthetics on rarely ever had issues unless there was a really bad polyester film pileup. Most never broke down again. Oh, and LaVezzi Oil in the intermittent. It's NLA, but a few dealers still have some on their shelves. Anyway... anything you use in the intermittent has to be non-detergent.

[Jacob Tutt]

Update: pivoting the shutter bracket assembly in has made a distinct improvement, but there is still some ghosting top and bottom on dark scenes. Swapping the fiber shutter gear looks like the next step

Lots of strobe apps for smartphones. How do I use the strobe to test for issues?

I am using Super Lube synthetic grease for the gears and Mobile one 75w-90 for the intermittent and sprocket shafts

[Mark Gulbrandsen]

75W90 is too heavy for the intermittent. What ever you use, it needs to be an SAE 20 equivalent. The 75W90 is about 40W... LaVezzi Oil was SAE 20W...

Is the lamp focused correctly, or are you spilling light over the edges of the shutter?

It's difficult to see the wear on the fiber shutter gear through the grease. Also when you change a fiber gear on a projector this old, also change it's mating steel gear.

[John Eickhof]

one thing to look at is the gear that drives the intermittent it has a key in it on the vertical shaft, the gear will get worn out internally on the keyway (GR234) if you hold the shutter fiber gear on the vert shaft then rock to intermittent flywheel, look to see if there is slop in the GR234 on the vert shaft, Personally, I would install a new GR-207 and the steel shutter gear GR7 (it looks undercut and worn to me) given the age of the model C these are normal replacement parts, I have NEW GR-207, GR-7, and GR234 gears in stock as well as BG-6 and BG9 precision bearings at very affordable prices, pm me