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ArriSun 1200 Plus with Magnetic Ballast flickers visibly


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#1 Tom Morrow

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Posted 25 January 2015 - 02:39 AM

I just bought my first HMI light, a used Arrisun 1200 Plus with magnetic ballast. I am seeing flicker with my naked eye which I wasn't expecting. I am curious if others have seen the same issue.

Here is the note I sent to the experienced gaffer that I purchased it from. He said the light was about 20 years old and he has owned it the whole time....

I want to ask your advice about the Arrisun 1200 HMI that I just bought from you earlier today. As soon as I fired it up in my dark apartment I noticed that it was flickering in a way that was easily visible to the naked eye. The flicker was reminiscent of old televisions or old fashioned mag-ballast office flourescent lights, perhaps about 60Hz. I don't remember having noticed this with other HMIs I've seen on set, although most of them were electronic ballast.

This persisted over the half hour I had the light on. Additionally there was a sort of irregular flickering every now and then sort of like a candle flickering in the wind which anyone would have noticed.

This did show up on my camera tests too, although more subtly than to the naked eye. I'm guessing I didn't notice it in your shop because the sunlight filled in the dark-flickers and I was looking for banding in my test clips not actual flicker.
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He wrote back kindly offering a refund if needed, and offering to let me test with different heads in his shop next week. He also mentioned that when he has seen such problems it was due to the circuit that it was plugged into. My apartment where I plugged it in was constructed about 10 years ago with all 20 amp circuits and outlets so I doubt it's the circuit itself, although I will have to check to see if it might have been on the same circuit with my computers and switch-mode-power electronics.

I'll be doing more experiments Monday or Tuesday, and I'm open to any suggestions.
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#2 Guy Holt

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Posted 25 January 2015 - 12:16 PM

I just bought my first HMI light, a used Arrisun 1200 Plus with magnetic ballast. I am seeing flicker with my naked eye which I wasn't expecting. I am curious if others have seen the same issue.

 

In my experience, flicker that you can see with your eye typically has to do with a loose connection in the power supply. Try rewiring the plug end because you might have some broken conductors in the plug. If it is the 1200 compact ballast, try moving the AC cord around next to the cable strain relief on the ballast.  If the flicker goes away in some positions but comes back in others, then there are some broken conductors at that point where the AC cord enters the ballast and you will have to replace the cord inside the ballast from the strain relief to the breaker.  To do so, cut the cord just before it enters the ballast and then thread the cord into the ballast through the strain relief and wire it to the breaker. For more details on how to trouble shoot HMIs see http://www.screenlig...gnetic Ballasts

 

Guy Holt, Gaffer

ScreenLight & Grip

Lighting Sales and Rental in Boston


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#3 Tom Morrow

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Posted 26 January 2015 - 01:58 AM

Thanks for that. Sounds like the issues you are talking about are generally high resistance from bad connections. I will try taking the lamp out and putting it back in the socket, to see if perhaps it had a bad connection. I do note that there is some pitting on the aluminum head which leads me to think these might have been exposed to rain at some point.

BTW that link doesn't work for me on iOS but I assume I can see the same thing by going to the

HMI lights with Magnetic Ballasts section in
http://www.screenlig...generators.html

What I got out of that is that it sounds like mag ballasts are supposed to output power pulsed at 120Hz to the lamp, probably by doing a full wave rectification on the AC 60Hz sine.

I remember back in the old days of CRT monitors that I could see flicker at frequencies that many people could not. I can't remember if the cutoff where I started not being able to see flicker was slightly below or above 60Hz but it definitely was not anywhere near 120Hz.

So I'm thinking perhaps part of the rectifier could be defective leading to 60Hz output instead of 120Hz. I suppose I could record some highly overcranked video to check that out.
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#4 Tom Morrow

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Posted 26 January 2015 - 04:26 PM

So here's my more general question: is it normal for HMIs to have visible ~60Hz flicker or is that a sign that the waveform going to the lamp from the mag ballast has an unusual/defective duty cycle with too wide a gap between pulses?


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#5 Tom Morrow

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Posted 29 January 2015 - 10:40 PM

So here's my more general question: is it normal for HMIs to have visible ~60Hz flicker or is that a sign that the waveform going to the lamp from the mag ballast has an unusual/defective duty cycle with too wide a gap between pulses?

I guess I can answer my own question here.  I read the HMI chapter in Set Lighting Technicians Handbook, and learned that yes magnetic ballast HMIs basically rectify the 60Hz sine power into 120Hz half-sine pulses.  So no the flicker is not 60Hz but there is regular flicker.

 

 

As to my irregular flicker problem, I did a lot of work and I think I solved it.

- Determined that the green ground wire in the outlet cable had a break in it, and replaced the cable.

- Determined that someone had swapped hot for neutral in the NEMA5-15 plug so it was wired unsafely, and fixed that while replacing the plug.

- Noticed a 220 microF capacitor on the logic board was bulging out as if it might be ready to blow, and replaced that.

- Blew and wiped dust out of the ballast wherever I could.

 

None of these things seemed to affect the irregular flicker, so continued...

 

- Unscrewed the reflector and blew and wiped dust out of the lamphouse

- Unscrewed the bottom plate of the head and the transformer cover, and blew and wiped dust out, while jiggling terminals to make sure they were seated well.

 

It seems that the blowing and wiping dust out was what did it.  I ran the lamp for four hours and only towards the end am I starting to see just-barely-maybe-perceptible irregular flicker.  I think it might be associated with the lamp orientation (nipple up IIRC).  So I will go in with a shopvac and make sure all the dust is out and reverse the lamp.  I suppose the high voltages inside the lamp socket especially could make arcing flicker, assisted by the dust of 20 years.

 

Question: can I walk into my film/lighting supply house and ask for lubricant that will withstand high temperatures so I can lubricate the rails to stop the squeaking when adjusting between wide and flood, or is there some special sauce I should know about?

 

And is there a suggested orientation for the lamp (nipple up or down)?  I suppose it probably doesn't matter since it looks like these lamps can supposedly be used in any orientation from pointing straight up to straight down.


Edited by Tom Morrow, 29 January 2015 - 10:40 PM.

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#6 Matthew Parnell

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Posted 30 January 2015 - 08:43 PM

Check your flood spot rails to see if they have lubricant on them already. Also check the rails and worm gear is straight and square, and all the adjustments are correct.

If the rails and gear aren't wet lubricated already, I use graphite powder on the rails and worm gear and work it in by flooding and spotting until smooth, then blow/vac the excess out of the housing.

Lampheads as you have discovered tend to get really dusty, and using wet lubricant on the flood/spot gear I find attracts that dirt/grit and you can end up with the lube clogging up.
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#7 Tom Morrow

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Posted 31 January 2015 - 07:05 PM

Thanks Matt.

 

I went to my local supply house and spoke with the guy who services Arri lights.  He said showed me the label of the moly lube that Arri has recomended to him and it looked like this:

 

http://www.amazon.co...E/dp/B00L42R48E

 

When I search for Sprayon S00200 I get this which I assume is the new label:

 

http://www.sprayon.c...t-aerosol-lu200

 

But he also showed me graphite powder and said that mixing it with isopropyl alcohol allows it to be applied without making too much of a mess.  So based on that and Matt's post I bought some graphite powder at my hardware store and will try that.

 

I've been continuing to test the HMI and ran it three hours with only one brief irregular flicker period horizontally, no flicker most of the time.

But when I direct the beam straight upward toward the ceiling I get some visible regular flicker, which seems perhaps 30Hz or less.

 

So my next step in diagnosing this is to buy a new lamp and see if the flicker goes away with that.


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#8 Tom Morrow

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Posted 31 January 2015 - 08:26 PM

I see that most websites say the correct bulb for the Arrisun 1200 Plus HMI head is the Osram 1200W/SEL/XS. But the bulb that Arri recommends in their literature is the 1200W/SE, and the bulb that was in my head was marked Osram 1200W/SE, not SEL/XS.

 

Does anyone know if the SEL/XS is the same as the SE, and if not what is the difference between the two? I sent this question to my dealer but figured perhaps someone on the net would know better.


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#9 Tom Morrow

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Posted 02 February 2015 - 11:47 AM

I got an answer to my question about the different lamps:

The SE designation stands for ‘single-ended’, while SEL stands for ‘single-ended lamp’. Those are just the terms used by each manufacturer to differentiate their products. The SEL/XS however does have a greater lamp life of approximately 1000 hours due to the eXtreme Seal technology to help withstand excess heat. On the other hand, the SE lamp only has a lamp life of approximately 750 hours.
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#10 Tom Morrow

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Posted 17 February 2015 - 12:10 AM

Ordered a sel/xs lamp from b&h. The lamp that I received said 1200w/sel but didn't say xs anywhere on it. I suspect that the xs is not supposed to show up on the lamp. I also learned that uvs is replacing xs so the next lamp I buy will be a 1200w/sel/uvs. Uvs means lowered uv output.

Anyway I now cannot reproduce the flickering issues with the old or new lamps now. I am not sure if the flicker just got burnt out or what but the flicker that was occasionally very bad is now not in evidence. I am guessing the capacitors are marginal enough that I should probably replace them but for $750 or so that Arri said new caps go for I figure I might as well wait and not replace until the flicker comes back.
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