Strong Super 80 / Arc Stability

[Ryan Gallagher]

Trying to chase down this issue next time I have a maintenance window.

Symptoms: Arc walks a little bit, causes perceptible intensity flicker/waver on screen with (bright scenes especially).

Caveats: Showing 25v on a 29v rated lamp. Amp Meter on that lamphouse is non-functioning, but Voltage reading button will produce a reading.

Can i just use a Clamp style amp meter on the lamphouse cable bundle and expect to get an accurate reading? Tuning the 25v up to the desired 29v appears to be the next logical step.
Long term, could I just wire in a digital voltage and/or amp meter and mount it to the lamphouse?

We do have some untested backup supplies we could also try that were scored in bulk many years ago also. But confirming supply rating, amp metering, and tuning voltage seems like the next step.

Things done so far:
- attempted to tune rectifier (without amp meter), no change other than we can un-strike the lamp on the wrong settings.
- Swapped to a new lamp, old one had a rusted Cathode pin, possibly better but arc still walks more than our other projector.
- Confirmed lamp house magnet is in place and does not appear jostled out of position.
- Cleaned corrosion and rust off electrical contacts at lamp and anode wire bolt.
- Have not serviced the control side/amp-meter yet.
- Checked shutter timing. Although this unit does have counter rotating shutters that does not appear to be the perceived intensity flicker.
- Supplies not showing any Ripple warning, but have not checked any other way.

Lamp info:
- Former: 4000w LTI LTIX-4500W-HS (211hrs only, 2018 manufacture, rusted in place slightly over 6 years).
- Current: 4000w Ushio UXL-40SC (0hrs but 2018 manufacture)

Supply info:
I will verify but I believe it is on a Strong 3-5k rectifier. But I do know there was a rating difference between the two installed in the booth. Will confirm it is not the 1-3k type (which would seem underrated for the lamp).

Cheers for any advice on next steps!

[Steve Guttag]

First step...stop calling it an "Amp Meter" It is an ammeter.

If the meter works for voltage, then it will work for amps. It is the most basic of basic circuits. The push button either puts the shut across the meter or it puts a series resistor between the meter and the power supply. As such, either the switch is bad or the wire (black) between the switch and the shunt is broken.

As for a clamp on ammeter...yes, those can be used and, if a decent one, are more accurate than that little meter/shunt. However, accuracy isn't that critical and remember, that is DC current...99% of the clamp on style meters you'll find are AC type meters. And, within the DC capable ammeters, you'd want one that goes up to 200ADC (for example, the Extech 390941). I'd try to get the built-in meter going before dropping that sort of "coin" on a 1-off tool.

Since it is a 4KW lamp you are working with, I'd make sure I was in its operating range. The nominal current on a 4KW is about 135ADC but Ushio has a wide range and typically tops out at 150A. I forget what its bottom end is but normally there is a sheet in there that will list the operating parameters of the lamp.

How well the lamp is aligned (centered and focused) and the lamphouse is aligned will factor into perceived arc movement. If you are catching the edges of the arc, you will have a more pronounced flicker than if the cone of light is well centered and focused onto the film. Note too, your projector, depending on the shutter style, could play into perceived flicker/arc wonder. If you have double-shutters, for instance (Century JJ, DA, CC, HH), the counter rotating shutters will not track precisely and give a bounce to the light that is not the fault of the lamp (the heavier the shutter material, the slower the movement of the light).

The style of shutter can also create a more pronounced pulsation to the light (it depends on where the shutter(s) are in the light path and their linear velocity, which is a function of size and angular speed.

And yes, bad power (particularly if the main filter capacitors have gone bad) will cause flicker and will also age the lamp by passing "ripple" to the lamp.

[Mark Gulbrandsen]

First step...stop calling it an "Amp Meter" It is an ammeter.

If the meter works for voltage, then it will work for amps. It is the most basic of basic circuits. The push button either puts the shut across the meter or it puts a series resistor between the meter and the power supply. As such, either the switch is bad or the wire (black) between the switch and the shunt is broken.

The switch is a 25 cent piece of Chinese junk. I've had to replace a couple over the years, one I remember was in an Iwerks 8/70 system. Also, I converted all the JJ's I installed over to single blade. May not be possible to easily do that now, because no one makes the parts any more. Hopefully they have switchers, and not the old Strong boat anchor power supplies.

[Ryan Gallagher]

Thanks Mark and Steve.

I'll investigate the switch being bad. It reads Volts on depress, but needle stays at 0 when not depressed (ammeter mode). Will get a better look at connections in the lamphouse, of which one wire definitely had e-tape on it already.

I already own a Fluke DC capable clamp meter with appropriate range... so that is an option too.

But all that said, as this IS IN FACT the unit that needs the most realignment too... we'll endeavor do finish that next, as Steve suggested it can exaggerate the visibility of the issue, an aspect I had not considered.

It is also the 4 blade counter rotating unit. It's partner is a dual blade regular shutter... making them match is also on the wish list. What we perceive definitely seems like not counter rotating shutter related, because it is also noticeable through the arc viewing port, but I could be wrong! Getting to those blades for a cleaning and check for slop is also on the bucket list.

Will investigate rectifier health last other than tuning it's output. Have others we could try.

[Steve Guttag]

While looking through the spot-sight glass on the shutter cover, on the double shutter one, you'll be able to see the line where the shutters converge/diverge. That line will have a bounce to it. It will give a clue as to how much the shutters are adding to the perception of flicker. If that line is bouncing a lot in height and relatively slowly, it will look like a wandering arc. If it has a much more rapid bounce, it could make it look like flicker...depending on how much it is moving.