Film-Tech Forum ARCHIVE: Rectifier - Fried, baked and toasted

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Posted by Barry Floyd (Member # 385) on 10-11-2010, 10:55 AM:

Lost the rectifier on Screen 1 on Sunday night. It's an older Kneisley "Kni-Tron" 3 phase unit. For several weeks we've had a burning wood smell coming from the projection booth on the screen 1 side, but never could track down where it was coming from. I even grabbed the step ladder and popped the ceiling tiles to make sure nothing in the attic was on fire.

Last night , about half way thru Alpha & Omega the picture goes from full brightness (as normal) to almost half as bright. I noticed it looked dim, but thought that the lights from the warehouses across the street were messing with us again. At intermission, I go into the booth, and the burning smell is back, stronger than ever and the amp meter on the back of the lamphouse (Kneisley Xenex II) was reading about 45 amps (it usually reads about 140 amps). The picture was still on the screen, but very noticeably dimmer than it should be. I called my projection technician and tell him whats going on and he suggested I shut it down immediately as to not cause any irreparable damage to the machine or worse yet the bulb. Since it was during intermission, I got back on the microphone and told the 10 cars that were there that we were not going to show the second feature and gave them all passes to come back another night.

After the machine cooled down, I threw the breaker to the rectifier and popped the lid on the top where the adjustable transformer taps are located. There was a HOLE burned completely thru the board where the taps are and the section where our taps were made had burned completely thru and had fallen down into the guts of the rectifier. The edge of the burned hole in the board was still smoldering and glowing orange.

My tech thinks it's possible that we either lost a diode or the wire connections at the tap bar had worked loose and caused it to catch fire. He's coming out on Tuesday to check it out and see if we can salvage the unit. If not, it looks like we'll be going shopping this week.

Tried uploading an image, but the server keeps rejecting me.

Posted by Martin McCaffery (Member # 37) on 10-11-2010, 11:05 AM:

Had the same thing happen to me on our IREM a couple of weeks ago. Connections had, I assume, vibrated loose and were arcing and heating the connectors. Had to replace the board and 2 cables, otherwise no permanent damage. No one smelled anything. Picture was fine until the unit just wouldn't strike at all.

Posted by Bruce Hansen (Member # 281) on 10-11-2010, 11:40 AM:

quote:
Topic: Rectifier - Fried, baked and toasted

I would think that "baked" would be healther for you then "fried" (sorry, just couldn't help it).

Posted by Richard Hamilton (Member # 321) on 10-11-2010, 12:01 PM:

Loose connections

Posted by Gordon McLeod (Member # 33) on 10-11-2010, 12:23 PM:

it is important to check all high current connections regularly

Posted by Monte L Fullmer (Member # 2797) on 10-11-2010, 12:47 PM:

Get an IREM for replacement for it will last a lifetime.

Posted by Tony Bandiera Jr (Member # 2365) on 10-11-2010, 01:46 PM:

Richard is spot on, that kind of failure comes from bad connections.

Kneisley's rectifiers have always been crap, and as a tech I knew used to say, Kneisley puts the "fire" in rectifier. [Big Grin]

Get an Irem as Monte suggested. Not only will it last longer, but it is very easy to service if needed.

As for the picture posting, keep trying, there have been times when I had to try up to five times in a row to get a pic to post (and it was withing the sizing guidelines.)

And I can't believe I'm saying this, but even a Strong switcher would be an improvement over the Kneisley.

Posted by Ken McFall (Member # 845) on 10-11-2010, 01:54 PM:

Don't knock the Kineisley.... how old is it? How has it performed during that time?

I've never seen one so have no experience with them but as in all things if connections work loose they will fail.

Bright and Tight was what I was always told and this is NEVER more true than with rectifier DC connections.

NO rectifier will run without problems if the connections work loose over time.... even Irem!

Posted by Gordon McLeod (Member # 33) on 10-11-2010, 01:57 PM:

i have had as many connection failures in Irems and Strongs as in Kniesly and we make it a policy to retightened all rectifier and lamphouse connections during each bi yearly service

Posted by Richard Hamilton (Member # 321) on 10-11-2010, 02:10 PM:

quote: Gordon McLeod
we make it a policy to retightened all rectifier and lamphouse connections during each bi yearly service

. That's what PM's are for, glad to see someone else practices that [thumbsup]

Rick

Posted by Louis Bornwasser (Member # 3063) on 10-11-2010, 02:58 PM:

Your tech should be checking high amperage connections during the routine maintenance check for tightness. That is part of the job.

It may be possible to repair your rectifier, depend on how much is burnt. I would guess that only one connection is bad and one wire. I would not just go buy another rectifier.

Still, what the say about the IREM is true. Louis

Posted by Mark Gulbrandsen (Member # 72) on 10-12-2010, 08:46 AM:

Almost every Kneisley rectifier I've ever encountrered has burned up sooner or later. There don't seem to be any exceptions either. On 1600 watt units it's always the transformers... on the other units it's either the transformer or the black connection board. It's literally a miracle that one hasn't burned down someone's theater and I can imagine how many times the fire departments have been called out for these. Amazingly, they produce really clean DC. ~ 6% ripple and very low inrush but at the expense of very high AC current draw... too little iron was put in these units!

Mark

Posted by Barry Floyd (Member # 385) on 10-12-2010, 09:05 AM:

quote: Ken McFall
Don't knock the Kineisley.... how old is it? How has it performed during that time?

We bought the unit "used" back in 2003, and it's never given us a bit of trouble in the 7 years we've had it. It's always worked when we flipped the switch.

Spoke with another drive-in owner and he said his did the exact same thing, and it was a loose connection - just like you guys have said.

Posted by Barry Floyd (Member # 385) on 10-14-2010, 08:42 AM:

Tech came in last night and got us up and running again. Like you guys said... loose connection on the bottom side of the tap board. The bolts that were there looked like they had been welded on by a high school shop class student.

Ended up cutting off the three old spade lugs on the tap wires, crimped new ones one, and ran a copper bolt through the new lugs and tightened them down with a lock washer and new copper bolt. He then wrapped the whole thing with electrical tape. He reminded me several times that this was only a TEMPORARY FIX until I can buy a new phenolic tap board assembly from my equipment dealer. Since we only have like 4 weekends left for this season, we'll probably wait until March when the money starts flowing again to have it re-done.

Thanks to everyone for their help.

Posted by Louis Bornwasser (Member # 3063) on 10-14-2010, 07:19 PM:

One "bonus" with Kneisley is low cost. Go ahead and buy the part you need & let your technician do this at leisure over the Winter.. . . . time consuming. This will give you time to test and repair if he gets confused. Louis

Posted by Barry Floyd (Member # 385) on 10-14-2010, 09:14 PM:

quote: Barry Floyd
He reminded me several times that this was only a TEMPORARY FIX until I can buy a new phenolic tap board assembly from my equipment dealer.

Good thinking Louis... and since you ARE my equipment dealer, I'll probably give you a call in a couple of weeks to get it taken care of.