Film-Tech Forum ARCHIVE: pro-35 got kind of dark? Shutter?

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Posted by Josh Mitoska (Member # 1086) on 02-01-2006, 09:59 PM:

My manager called me tonight to let me know that the picture became suddenly darker in my #1 auditorium, He checked the dowser and it is ok, checked the lamp ok, he then took the cover off behind the framing lever to see if the shutter fan was loose, it was tight. He rolled some film through by hand and one of the fan blades would be in front of the light while the intermitenent gear moved, but then the other 3 fan blades would not be over the light when the intermitent moved??? So how is that possible, the darkness on the screen was coming from the shutter being off but off 3 times out of 4, he checked several times and it was always the same 3 out of 4, the same blade each time was the right one that was on- What do you think happened???

Posted by Mark Gulbrandsen (Member # 72) on 02-01-2006, 10:16 PM:

An all of a sudden darkness shift that does not have any smearing or travel ghost to the image could be due to several things. Two things that come to mind..... A lamp that suddenly shifted position and changed lamp focus or X-Y. Or a lamp that has gone gassy usually indicated by a bluish-white coating inside the lamp. Something blocking behind the aperature... dust, crud, film chips. From the way you dscribe your shutter it sounds like a 3 bladed type, of so these also cut down the light level. a 3 blade would be unusual but not impossible in a full time theatre but common in screening rooms. If the shutter had gone out of time there would be at least some smearing or travel ghost to the image. If white titles on a black background are nice and sharp then the shutter is probably ok.

Oh, and check the lens end of things carefully too!

Mark

Posted by Monte L Fullmer (Member # 2797) on 02-02-2006, 02:08 AM:

How about that idiot center hindged dowser around the shutter shaft that is held up by that selinoid that there has some relay circuitry in the PROS that loves to close that dowser without any warning.

Fought one of those in Rock Springs for quite some time until I found a relay that was acting up. Danged thing, for three to a dozen times, would just slam shut during a show. First time, I would just disonnect the rod that runs from the selinoid and wire the dowser up until I could "buglight" the thing out - where it pointed to that relay and finally took care of this idiot problem.

-Monte

Posted by Thomas King (Member # 2745) on 02-02-2006, 06:30 AM:

Do take a close look at the lamp. It's possible for a lamp to still be striking/running okay but putting out drastically less light. Happened to me during a show recently; thankfully no-one (all seven of them) seemed to notice.

Posted by Josh Mitoska (Member # 1086) on 02-02-2006, 08:14 AM:

Would it be possible that the power supply could be putting out less power than normal and not giving the bulb proper power? My manager said the power supply sounded different also, it is usually quite noisy, and he said it changed to a quiter deeper hummmm

Posted by Mark Gulbrandsen (Member # 72) on 02-02-2006, 08:20 AM:

quote: Josh Mitoska
Would it be possible that the power supply could be putting out less power than normal and not giving the bulb proper power? My manager said the power supply sounded different also, it is usually quite noisy, and he said it changed to a quiter deeper hummmm

Absolutely! Check your operating current.....

Mark

Posted by Josh Mitoska (Member # 1086) on 02-02-2006, 08:39 AM:

Mark- I'm not sure how to check the operating current? Is that from the back of the projector?

Posted by Gordon McLeod (Member # 33) on 02-02-2006, 08:41 AM:

well he did say the dowser was operating properly so that rules that out and he also said the lamp was ok so maybe it is time to call in the engineer and get to the bottom of the trouble

Posted by Josh Mitoska (Member # 1086) on 02-02-2006, 08:42 AM:

I just called the manager from last night, he said the piece on the back of the projector was readign at 25 volts??? And the two upstairs projectors were at about 75- , So are you thinking this is a power supply problem? I'm not familiar with repairing a PS or knowing how to check them-

Posted by John Pytlak (Member # 331) on 02-02-2006, 08:57 AM:

Yes it does sound like it may be a lamp power supply problem. Since you and your manager are not familiar with diagnosing or safely working on electrical problems, time to call in your service engineer, as Gordon suggests. Working on a power supply or ignitor are very dangerous if you don't have the knowledge, skills, and experience to do so.

Only one blade of the shutter actually blocks the light as the film is being pulled into position for each frame. The other blade(s) are called "flicker" blades, and are needed to raise the shutter flicker frequency to 48 or 72 interruptions per second to avoid the severe flicker that a 24 interruption per second rate would have.

Posted by Gordon McLeod (Member # 33) on 02-02-2006, 08:57 AM:

call in the engineer if you are unsure of what you are doing as you could injur yourself or others

Posted by Dave Macaulay (Member # 813) on 02-02-2006, 09:00 AM:

If the lamphouse meter is reading 25 and the others are 75, this is amps not volts, then the lamp would be very very dim indeed.
Probably a power supply problem, and possibly your lamp is being damaged as well by excess AC ripple on the DC power.
What power supply do you have? A Strong switcher can do this if the current adjusting knob cable comes loose, not uncommon. Rectifiers like Sanrex with saturable reactors go to low current if the control circuit fails. Brute force rectifiers like Strong, Kneissley, Irem, etc. all make give low output if a line phase drops out (on 3-phase types), if some wiring inside burns out, or if a diode fails; these failures usually also cause high AC ripple. But you should see that ripple as a slow flicker on screen.
So, check the rectifier connections. If there's no problem obvious, I suggest you call someone qualified to work on rectifiers and not open the case yourself; the internal voltages can kill you.

Posted by Josh Mitoska (Member # 1086) on 02-02-2006, 09:07 AM:

I will call a tech then , that seems best...Thanks for all your help, I'll post what happens-