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Author
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Topic: Another rectifier story
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Harry Robinson
Expert Film Handler
Posts: 155
From: Franklin Tennessee
Registered: Dec 1999
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posted 07-30-2001 10:44 PM
I'm pretty sure God is testing me to see if I really want to get into this hobby. I have an old H-10 Christie. This is the 1K lamphouse that works on regular household current. When I got it, it was filthy inside. I cleaned it up, called the local tech to help me, and we had it up and running in no time. It had the bulb that came with it, and we had no way of knowing how many hours were on the thing.It worked pretty well as we got the screening room together. Finally we got close to completion, so I bought a brand new bulb. Whoops. The bulb seems five times brighter than the old one. The H-10 rectifier has three power settings, so we set it to the lowest one. The tech recommended this. It was still really bright on my 5 1/2' X 12' screen. One night I had it set on high when we began to smell burning insulation. We went back and looked at the rectifier and smoke was coming out of the top vents. I called the local tech and he came out. He opened it up. He said there were some bad connections, and the thing looked like it had been jerry-rigged. He took a whole day, put in new internal cable where it had overheated, hooked it up, and ran it. Everything was just fine. Two weeks go by. I get the new Super Head with the three blade shutter. We need more light. I turn the rectifier on high, and sure enough she begins smoking. The tech won't be back in town for more than a month. I'm willing to crack this thing open, but I'm filled with fear and loathing. I know not to get near the capaciter or touch it while it's plugged in. Do you guys think this thing just has another bad connection? Will tightening down the places where it looks like it was burning help? I can put new cable in there, but it just seems like this could be something a little more serious, and I don't want to aggravate the situation. The nice thing is that no matter what is wrong, the chances are it can be fixed. I hope.
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 07-30-2001 11:13 PM
On old transformers, the thin varnish-like coating around the wire (on the primary or secondary) can break down and short from layer to layer. I'm wondering if the "high" power setting uses a tap off of the transformer, that's not used otherwise, and that section has shorted windings.Can you see where the smoke is comming from? Did the tech try it on "high" after servicing it? When switched to "high" does the lamp get really brighter (or only a little?) Try taking off all the covers and turning it on to see what's happening (be careful!) If the windings are shorted, many older transformers can be disassembled and rewound. It's labor intensive, but if you can't justify the money to replace it, that might be an option.
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John Anastasio
Master Film Handler
Posts: 325
From: Trenton, NJ, USA
Registered: Sep 2000
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posted 07-31-2001 07:20 PM
Smoke is a wonderful visual and olfactory indicator of component failure. Isn't it amazing how just a few parts per billion of grilled insulation in the air can make your nose stand right up and say "whoa!....we have a problem, Houston." My electronics mentor back in college taught me the technique of "TMS"; when your back's against the wall and you're not sure which component is failing, turn the thing on and TMS...tune for maximum smoke. One thing's for sure...you'll know exactly which component has failed. You won't always know the cause, but you'll have a really good idea of the area you need to fix. Turn the thing on, TMS and shut it down as soon as you can see where it's coming from. If the transformer has shorted, you should be able to see heat damage if you can see the core. My Communications Technology students inadvertently TMS quite frequently when they're working on new projects, then want to know what they should fix first. I always tell them to use their nose! About the only thing you're changing when you hit that power switch is the winding on the transformer, so I suspect that's where the problem lies. If the trannie's bad, pull it and rewind it.
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Rick Long Jr
Expert Film Handler
Posts: 211
From: Toronto, Canada
Registered: Jul 2000
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posted 07-31-2001 08:34 PM
I'm not familiar with that model. Is the power supply built into the lamphouse like those little ORC models, or is it a separate unit?
I'll assume that you are using a 1000 watt bulb. Is there an ammeter? If so, you should use the setting that gets you around 50-55 amps D.C.
If the picture is too bright or dim I would recommend adjusting the bulb focus and bulb(or reflector) position controls, as opposed to adjusting the current. As to what the problem could be, it has been my experience that when a rectifier smokes, it is usually a bad connection on the D.C. end of things, though not always. Transformers can burn up, especially if too much current is pulled through them. Chances are, as John said, the output knob selects different taps on the transformer. If one is a little flaky, this could be the cause. Try the lower settings. Does it still smoke? You mentioned "tightening down the places where it looks like it was burning". If you see burned connections I would say that is a very good place to start, though just simply tightening them may not be enough. I recommend taking them apart and cleaning the contacts with some emery paper.(Be carefull where the metal filings go!) If the wire is long enough, cut back and get rid of the burnt chunk. If not, you may have to replace it. Also check the diode connections. I don't know how accessible this unit is, but if you can open it up and turn it on, it should be obvious where the smoke is getting out.BE VERY CAREFULL though. If you don't feel confident about cracking it open, its probably better to call for help. On the other hand, it could be a simple fix. Good luck!
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