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Alain Bourassa

troubleshooting a weird 2.5K Strand (IREM) HMI ballast

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Hi guys

 

Looking for new ideas here , I'm an electronic technician with 25+ years of experience , working with HMI since the mid 90's I also work as a DIT and Engineer

 

I was on a set last weekend, shooting outside on a very humid day

one 2.5K HMI Par was outside and the ballast did a flash and me and the DP heard a sparking sound when it happened

the light stayed on but once we turned it down it never responded to the ballast later on

the lamp is an old Strand Quartzcolor and the ballast is a magnetic ballast , Strand brand , made by IREM (same guts as the ARRIs)

 

My first guess was a blown capacitor inside so yesterday back in my workshop I opened it , replaced the 2 main electrolytic capacitor on the IREM pcboard and the main power cord too which was very brittle, I used gauge 12 wires as usual

 

tried the ballast with the head we had on set, it strikes and after a few minutes I see a lot of flickering and I'm hearing a loud hum from the ballast, like a AC to DC rectifier only working on half the phases

 

tried the ballast with a second head it strikes but does not stay on but the lamp works well with my other 2 ballasts of the same model

 

tried the same ballast one more time with a third head it strikes, light goes on and no hum no flicker ! like a perfect combo

 

I used the same cable on the 3 heads too so the cable is discarded as a possible problem source

 

I have never seen such a stubborn ballast in my life

 

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fixed !

after reading my own thread here I had an idea and I went back looking at the logs of the lamp

the third one had the newest bulb, the one striking but not lighting had the oldest one and the noisy working one is in between

so I guess not enough current and I took a close look at the capacitor bank under the transformer inside the ballast

 

and that's where I found the real problem !

they are wired in parallel

11781616_10152873712951627_1846950983853

 

11694970_10152873712981627_8533429465545

 

and on the first one of the top row the soldering was melted the wire was not touching anymore , so only half of the capacitors were available !

newest bulb requires less current so it was working, the older bulb didn't have enought current when it was putting more lights that's why there was so much hum and flickering and oldest bulb was not even striking properly because of a lack of current

 

I redid the soldering and everything works now

11703142_10152873712911627_7285976365593

Edited by Alain Bourassa

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Why did it melt? Without knowing the cause it may happen again. Enough heat to melt the solder joint from?? Excess current flow in too small a conductor??

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Why did it melt? Without knowing the cause it may happen again. Enough heat to melt the solder joint from?? Excess current flow in too small a conductor??

 

the ballast is old ,at least 20+ years old, and we were outside, very humid, the ballast was on the ground on top of a small apple box

I think there was not a single reason why it sparked there but an ensemble of conditions put together

I have to admit in my life as a rental house technician I never had to go that deep inside a ballast

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