Lamp un-strikes (Strong Super 80)

[Mark Gulbrandsen]

"

Here is an additional thought. Could it simply be a bad Cathode connection, that gets worse with thermal expansion?"

Yes. If you have a bad high current connection, either positive or negative end they usually discolor because they can get literally red hot in very short order. You would also see it on the pin of the lamp. Check all the high current negative wiring with an LED flashlight.

"The problem "First" occurred literally as I manipulated the lamp focus position. It then persisted occurring with that original lamp (would strike but then later start to restrike or extinguish). We chalked that timing up to coincidence at the time, assuming a good cleaning and lamp swap might solve it."

Get a very bright LED flashlight and carefully check the rear of the lamphouse to make sure a connection is not lose. Also check the connections to and from the DC shunt the feeds the ammeter. The LED flashlight will make it easier to see any discoloration in connections.

"As we changed to the new lamp we wire-brushed out some rust from the Cathode collet and copper tongues, and cleaned it as best we could with tools at hand. Similar for the bolts on the anode and cathode leads with the addition of some CRC contact cleaner. But the problem remained."

All the connectors are generally made of brass, not steel. They are sometimes chrome plated. Not so sure that was rust.

If that is a possible cause, Is there any other product or method I should use to really improve the copper and clamp negative cathode connection? It's definitely clamped fully, but not trusting we got it clean enough? A similar cleaning method worked on our other projector, which had an even rustier cathode pin, but then it never had this issue either.

I always used a tapered fine wire brush that I carried in my tools. What you may have thought was rust may have been overheated brass particles.

[Ryan Gallagher]

I always used a tapered fine wire brush that I carried in my tools. What you may have thought was rust may have been overheated brass particles.

I just ordered some Lincoln Electric emory cloth (320grit) and may give it another once over on tuesday. We did have a tapered wire brush, though it was a bit stiff to get into all the crevices. I say rust simply because it was evident on the old lamp pin too. But in general gunk to remove.

[Mark Gulbrandsen]

Wrap the emery around something round so you can do an even clean up... also check the tightness of the bolts that attach the heavy cables. And seecif it seems like any have gotten really hot in the past. Do the same with the connections at the rectifier. If the DC cables plug in to the switcher, then pull the plug and examine the high current pins for overheating. We already covered microswitches and down drafts, and I agree with Brad's idea of swapping the switchers between projectors. The big switchers rarely fail, but anything is possible.

[Randy Stankey]

I always used a tapered fine wire brush that I carried in my tools. What you may have thought was rust may have been overheated brass particles.

It could be plague. It doesn't have to just be silver. Even gold can develop plague. Almost any metal can form allotropes if kept in the right (wrong) conditions. Once metal starts to oxidize and form allotropes, there is virtually no way to stop it. The only way to resolve the problem is to replace the affected part.

If you are getting corrosion on your lamp connections, the wise thing to do is to scrap the offending parts and replace them with new.

If you don't, the plague may spread through the whole machine.

[Mark Gulbrandsen]

It could be plague. It doesn't have to just be silver.

If you don't, the plague may spread through the whole machine.

You actually think Strong would use silver? LOL! Only back in the Carbon days when it was actually Strong. And even then mainly on lamps that had rotating carbon's, because those carbon jaws were solid silver. Ditto for Ashcraft Carbon lamps.

Most of the stuff I encountered was chromed brass alloy of some sort. Copper, unless perhaps it's an alloy of some sort is too soft. Alumnium may have been used for some stuff because it's a very good conductor.

[Randy Stankey]

Many metals, including tin, copper, zinc, and even gold can form allotropes. Frequent temperature changes accelerate the process.

When tin solder connections turn chalky and gray, that's not just oxidation. The tin is actually changing its structure at the atomic/molecular level. Fortunately, for tin, reheating a solder connection can restore the metal to its original state.

Yes, I understand that it doesn't happen all the time and, when it does, it's often a slow process. You can often simply clean the parts in question and put them back into service but, in reality, it only buys you time. It might take months or years but, once it starts, it often can not be stopped. You will eventually have to replace the part, like it or not. Since the process is self-perpetuating, by the time you get around to replacing a bad part, it might spread to other parts of the machine.

I also understand that my job in manufacturing for critical applications like military, medical and aerospace makes me have to be on alert for problems like plague about a million times more than most others need to be. I knew about plague before I started working there but I didn't understand just how dangerous the problem could be if it goes unnoticed. I'm simply trying to get more people to notice.

It really bugs me when people seem to think that problems like this are important for things like fighter jets but not for movie projectors. It's just as important. It's just not as critical. I think that, if you see corrosion on electrical connectors inside a projector, it's okay to clean them and keep going but, once that's been done, the wise person will order replacements so that, the next time he visits that site, he will have them at the ready.

[Ryan Gallagher]

I had time today after we got our talent settled to clean the rectifier grill and fans, CRC Contact cleaned and inspected MS connector etc, no signs of issues there.

Same stability issues but noticing a more nuanced behavior.

When lamp is on it will sometimes “bounce” between 100ish Amps and the normal 125-130ish. I could visibly see a brightness change that clued me in. Prior i thought our ammeter was just being flakey when it occasionally displayed 100ish. When it extinguishes we are still 4-Green on the supply, confirmed.

But when it extinguishes it is typically from that lower state.

Does that point in any particular direction?

Still have the real maintenance window Tuesday.

Unfortunately swapping supplies will be non-trivial. One is direct tie in, the other is adapted to an MS connector etc. I’m still hopeful that it is a cathode connection issue that might be resolved with round two of cleaning.

[Randy Stankey]

I would expect the current to fluctuate, a little bit, during operation but not that much. Plus or minus five amps, maybe. Dropping by a full 25% definitely signals a problem!

If the current drop occurs, gradually, as the movie is playing, my first guess would be that heat is the cause. Either a failing component such as a diode (I understand you have switching rectifiers...just an example) or a bad/corroded connection, somewhere.

An IR thermometer or a FLIR camera might help you ferret it out. Use your other, working, projector as a baseline and compare that to your malfunctioning one.

[Ryan Gallagher]

I would expect the current to fluctuate, a little bit, during operation but not that much. Plus or minus five amps, maybe. Dropping by a full 25% definitely signals a problem!

If the current drop occurs, gradually, as the movie is playing, my first guess would be that heat is the cause. Either a failing component such as a diode (I understand you have switching rectifiers...just an example) or a bad/corroded connection, somewhere.

An IR thermometer or a FLIR camera might help you ferret it out. Use your other, working, projector as a baseline and compare that to your malfunctioning one.

Randy, The drops are not gradual, and it is not a progress towards extinguish, it will drop those 25amps instantly along with a visible light shift, and then recover, and maybe do that a couple more times before it extinguishes. It may restrike quickly but the cycle repeats, if it restrikes at all in a timely manner. The time from first strike (which it has no problem doing) to 1st extinguish is reliably less than 10 min.

It is out of commission, no films booked at the moment, just trying to get things ready for summer classics. Bad contacts or looking for thermal issues are suggestions that are appreciated. Gonna go through my other short list first before I borrow someone's FLIR or buy the iphone attachment.

[Randy Stankey]

I can't be certain but I still think that connections should be checked. Even if it turns out that it isn't the case, you have, at least, eliminated one possibility.

[Sam Chavez]

I don't know what version switcher you have but I've some of these apart and was amazed at how many loose internal connections I found. Did not fill me with confidence. I'd say they're one or more loose connections somewhere.

[Mark Gulbrandsen]

I don't know what version switcher you have but I've some of these apart and was amazed at how many loose internal connections I found. Did not fill me with confidence. I'd say they're one or more loose connections somewhere.

You mean like this one I found in a Version 1 switcher? It got hot enough to melt the solder they put in the crimps... BTW, Version 1 switchers can not be repaired, as the semiconductors are obsolete in them.

[Ryan Gallagher]

After a few more hours spinning our wheels this morning, I supposed we have arrived at a point where it is time to crack open the supply and look for issues there, or phone in our local tech.

Today's efforts and outcomes:

• Pulled lamp, re-cleaned all high power DC contact points with emery paper and contact cleaner or alcohol, including the igniter lead behind the upper shield, and the shunt-resistor terminals. The brass and copper now look excellent along the whole high current DC path, as a bonus, the lamp now inserts without a herculean forearm battle. Cleaned up the supply grounding etc. Generally got deeper and checked terminals and tightness below at the barrier strip etc.
• Metered supply legs, all three showing 125v.
• Set up dedicated lamphouse metering. Voltage via annode and cathode spades on the igniter lead and strap post at housing. For Amperage we added two sense leads on the shunt resistor and also snaked them out of the chassis. In addition we were able to access one leg of the DC coming out of the supply for my clamp meter as a confidence measurement.

Initial re-test. Same story. 125-130A and 26v (confirmed via real meters this time) for about 5-10 minutes until things warm up, then we start to get the amperage fluctuations between 90-130A. When it extinguishes it might come back as high as 160A on an auto-restrike (beyond lamp spec). Supply never leaves the 4-Green status, and generally follows that unstable pattern from there until one of the extinguishes seems to stick for a while.

At some point long past our technical director picked up a pallet of strong switchers from Film-Tech (2017 it seems), probably last time they were having issues with one. We decided to re-test the 3 that were set up to direct swap because those 3 had the MS terminations and 3phase hubble already. At least one had a note that said it shuts off as soon as you strike the lamp. Was a mix of 3-5k and 3-7k units.

• Indeed. The 3 we tried lacked the spot/console switch, but they all exhibited this same behavior: "Xenon On" lights up as soon as they are powered (not expected), and a manual "ON" for a strike will trigger the supply to cut off entirely. In glancing at the manual perhaps there is a control board switch setting that would cause this? I'll have time to open one Thursday and see what position the board switches are in.
• Went back to the original supply. Decided to give it one last go with a 3rd "known good" lamp. (Prior pull from the other projector). This one exhibited same behavior as the other two. Definitely not lamp issue.

Today's conclusion. It's most likely in the power supply itself. Because the issue takes a few minutes to appear i'm leaning towards some component or connection level thermal issue. And our easily connectable spare supplies are either mis-configured or have their own (different) issue.

We did not go down the road of using our only "known good" supply to test it yet, as that involves re-doing the wiring harness that is adapting it to the MS connector. No one is eager to poke at the one projector that is happy right now. But it may be warranted to get a final verdict on this suspect supply.

The call is out for our tech, and I'll have more time Thursday to see if the unproven "spare" supplies are just configured wrong, and perhaps retry them.

Edited to add the man page with the switch positions:

[Ryan Gallagher]

It's worth adding that between supply swaps we did move the current trim, and once back on the original supply it was easy to tune it back to 130A using the clamp meter reading. I'll be using that method indefinitely. The voltage drop across the shunt worked great too, just more math.

[Tim Androes]

a couple of questions for you, Ryan
1) what model of Strong switcher are you using? i know you said R series but what is the full Strong product number from the data plate on the side of the unit?
2) you read 125 vac on the three legs but what are you reading across the legs? A-B...A-C...B-C Are you reading this at the terminal block just inside the rectifier?
3) have you checked the three-phase breaker in your main breaker panel? years ago I once worked several hours on an IREM high-reactance rectifier to no avail only to go over to turn on power to it one more time and then hear the breaker itself start crackling. one of the connections at the breaker was hanging on by a thread, just enough to register 125/leg at the rectifier but not enough when any load was applied.