What Dave was saying about the air jets was very understandable. I have one question though: Is the Lack of air pressure at the rotor gaps during ramp up the cause of those Strange scuff marks on the film shortly after the Picture Start frame on the Acad. Leader??? My boss is always talking about how bad it would be to lose air pressure during the show, But I think that vacuum would be more critical. But, I could just imagine how badly the film would be scuffed if the projector was to lose air.
Oh and one more thing, He also says that our machine is capapble of running 48Fps, but I am not sure about that. I can see no marks on the Cam assembly to determine if it truly is capable. Can anyone tell me what to look for???

I've not used a Classic, but both the GT and the SR have air as soon as the rotor starts turning. I don't see why the Classic would be any different, but apparently it is.

Rotors are very unique in that some will scratch film easily without air and some won't. In Tulsa, the SRs didn't; in Dearborn, the GT didn't; here in Grand Rapids, the SRs do. A lot of factors apply here, including booth humidity and the application of PhotoGard.

Here's a sample of an air jet scratch. It's in the shape of an arrow pointing away from the direction of film travel (picture is upside down); individual marks can be light to the point of be unnoticeable or heavy enough to dig through the emulsion. The rotor side of the film is rubbed against the air jet when the center of the film is bowed as the loop forms. The edges don't scratch because the stators and rotor segment rails don't let the film go anywhere it's not supposed to be.

Losing air pressure during a show will scare the living crap out of you. It will also severely scratch film on the air jets if you have one of those rotors that scratch film when you turn it by hand. When a GT E-stops, it immediately turns off the rotor air; on an SR, the entire system remains powered until the rotor has stopped.

The vacuum isn't as important as the air jets are (regarding scratches). All the aperture vacuum does is suck the film against the registration pins and hold it against the field flattener to be projected. I have not seen film damaged due to lack of vacuum, though I haven't exactly conducted a scientific study. I have seen an SR run without a field flattener, though the picture was all over the place and it made quite a racket. I wouldn't try that one at home.

Somewhere I saw pictures of a GT-HD projector and seem to remember a bit of extra stuff under the hood. I don't know what changes would be necessary on a Classic, though I'm sure Gordon could answer that one. I think his projector has probably seen other frame rates.

Got a few other questions about the system.

Does Imax make a Cue detector system that can be retrofitted to the older projectors so that you can place projector stop cues on the film?? I have seen a projector tail out once - not a pretty sight.
Additionally - My supervisor is considering a DDP II system to replace the DTS and Dubber - Would this be a cost-effective way to improve sound quality? Right now, when using DTS - we cannot add trailers to the film unless DTS has put them on the CD along with the feature soundtrack. We had used a D-TAC system in the Boise Imax, and I was very impressed with the Showlist setup.
My concern is this - On a new system, the D-TAC is tied into the automation of the projector and can control show start and ligts etc..... So how easily is the new system adapted to this old Projector with no automation whatsoever?

One more question:
My boss has asked me to find a way to set up a switch to change between the DTS system and the Dubber. Right now we have to go behind the Rack and change some XLR's and the Tach connection. I was thinking about using a bunch of P&B relays to do the job and have them all tied into a toggle switch. But, I am worried that the relays will introduce some Hum into the system. Any suggestions would be appreciated!!

Another imax question. On our old projector (relay based) the rotor air pressure gauge reads 0 psi when the projector is running, but when the dowser is opened, then the pressure jumps up to the normal 60psi. My question is: is this normal for this era of projector, and, would running the projector with the dowser closed damage the film?

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There is a definate change in sound when the dowser is closed. And there is noticeable marring on the film after the credits, because the dowser is closed at that point. The dowser button on the projector console is not functioning at this point in time, instead we are using the "Dowser Test" toggle on the back of the lamphouse. The problem is supposed to be fixed at next service. I hate to say it but the projector is very problematic. There are a few problems that I have experienced that make starting a show a very nerve-racking time. For instance:
Sometimes at show startup the dowswer will somehow open itself, thus showing Acad. leader on the screen. The only way to shut the dowser is to flip the toggle switch up and then down again. At that point the lamp shuts off for some strange reason. So that causes the need to re-strike the lamp.

And- sometimes in the morning when things are just getting turned on, The "system on" button does not work. It does nothing. The solution is this: I open the MKII reel unit, turn the local disconnect switch off in the bottom the reel unit, and then remove the positive battery cable in the top of the reel unit. I wait a few seconds, replace the terminal, switch the reel unit on via the local disconnect knob, and hope for the best. Usually it takes a repeat of 10 times to get the system to power up. The IMAX techs are stumped by the problem.
I suspect that it is in the E-Stop system somewhere.

Going from SR projectors to the mammoth old beast is a hard change to deal with. Maybe I should quit whining and just deal with it

My boss must have been blowing smoke, but if you go to BMZ the only print listed is the one at Spokane.
"Man Belongs to Earth" was the premier show for Expo '74 wasn't it??

Tristan

Who is your regular IMAX tech? Have you spoken to them about the air pressure oddities?

Since having the SR 's installed here 3 years ago some of the niceties of what air pressure gauges did what when on ole system 34 have fled from my brain. Be thankful you have an external pressure gauge. There are none on SR projectors.
We had a problem 2 years back when the rotor pressure dropped and film got scratched.No alarm. The only air pressure alarm is on the main supply.

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We have spoken to the Tech about all the problems listed. The rotor air gauge situation does not seem to be a big concern to him. I am hoping that the problems can be fixed on the next service call.

The SR projectors are equipped with a Rotor air pressure gauge. It is located beneath the projector cover on the left hand side of the projector. Why they decided to put the gauge out of view of the operator is beyond me. I have seen a "Rotor air pressure low" alarm on the system in Boise. The system was installed in '99. I can't imagine that there is an SR projector out there that does not have some sort of warning device to alert the operator of low rotor pressure. Everyone is familiar with the usual beep-beep of the "Air Pressure low" alert that is displayed when the air tank is drained at night. That system will even warn you if you lose 1 of the 3 phases of power supplied to the rectifiers.

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