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Best wishes for 2025. The sound of my Kalart 80-25 works for about 10 seconds and then starts to fade out until it is no longer heard. Can you tell me where I can find the audio circuit. This model is transistorized. Thank you very much for your help.
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KV 80-25 amp schematic_compressed (1).pdf
I can e-mail you a slightly better quality version if necessary. I had to compress the original to include here. -
Thank you very much Rich for your quick reply.
If you can send me an uncompressed version by email or wetransfer that would be better. I tried to improve the image quality in Photoshop without success. The title of the circuit says: "See Page 12 "Amplifier Electrical Check Points". It refers to a manual, do you know which one? I don't have any manual for this equipment and I couldn't find any information about it in the warehouse.
Thanks.
JuanComment
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Even without the enhanced schematic, I can get you started. Change ALL of the electrolytic capacitors on the amplifier board, especially the ones in the signal path. Aged capacitors will be out of tolerance and/or drift to open or short circuit as they warm up. With the age of the Kowfart Victim projectors this is you most likely culprit.
AFTER changing all of the caps, try the amplifier again. if it still fades out, the next thing ti look for is something getting hot (usually a transistor). If you have a thermal imaging camera or IR thermometer (which is cheaper) look for anything getting hot, If you have neither of those options, CAREFULLY touch transistors with you finger tip (Keep your other hand in your pocket and don;t touch any other part of the projector or any grounded object. Anything that gets so hot you can't touch it for a least a few seconds is the faulty part.
If you find a transistor getting hot, check all surrounding components for shorts or out of spec values (more that 10% off.)Comment
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Back in the day, we used freeze spray to identify overheated components on a circuit board. It's, basically, canned Freon. (or some such refrigerant stuff)
Spray the board with refrigerant until it starts to frost up. Turn on the circuit then watch for areas that thaw first.
This is one such product:
https://www.techspray.com/using-free...ty-electronics
It's cheaper than buying a FLIR camera unless you've already got one... unless you just want to have an infrared camera. In which case, go for it!
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Thanks Tony for your reply.
I fully agree with the repair procedure and I will do it that way.
Since I live on the other side of the world, I first want to know what components the circuit has, mainly the transistors, because sometimes it is not easy to get a spare part in this part of the world.Comment
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Randy,
Back in the day, I used freeze spray too. It is a great help.
ThanksComment
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In the Warehouse here on F-T, there is an 80-25 operators manual, I also posted the voltage check paragraph from that manual. Check each voltage test point to be sure it is within about 10 to 15% of the stated voltages before doing anything else. While it should certainly be recapped as Tony mentioned, I'd make sure that everything else is OK first, if you have bad transformers or connectors or the exciter circuit has issues, then that'll also need to be fixed. I have seen a lot of Nylon connectors in 16mm projectors fail, they often turn brown. I used to work for a school district that had over 600 16mm projectors, Kodak, Eiki, and a few Hell & Bowells. We stocked a couple of each pair of all the nylon plugs for those projectors in the stock there. Anyway, good luck... Kalarts are supposed to be very easy on film, and are popular with collectors.Comment
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Mark,
I found the manual for the 80-25 at Warehouse F-T. Thanks.
The Kalarts was forgotten for many years. Last year when I first turned it on, it had no sound. The problem was the aged speaker wire, the copper was "green". I replaced it and now I'm having the problem of sound fading.
As you say Mark "I'd make sure that everything else is OK first".
I think it's going to be a repair that takes time and patience.Comment
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Juan, if you PM me your e-mail I can send you the full size scan of the amp schematic. When I read your first post I pulled that page from the full service manual and scanned which is why there is a reference to "page 12" at the top. I do not currently have the whole manual scanned which wouldn't help your amplifier anyway. Maybe some day I will. Here's a tip: since the 80-25 uses a solar cell pickup for the sound (the RCA plug going into your amp), a standard microphone preamp will give you a signal that can be used by any HiFi amp you may have laying around and actually sounds a lot better than the stock stuff. I've had mine direct into my home theatre surround sound system for years and it's the only way I'd ever use it. Of course, the original amp must still provide proper voltage to the exciter lamp for this to work.Originally posted by Juan Andrés Cetkovich View PostComment
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That is very true Rich.... Many theaters in Chicago used el-cheapo McGohen Mono PA amplifiers for years before they conmverted to stereo. They were reliable... the company had been around since 1946.Comment
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If you have seen green wires, you probably have a case of "plague." Over time, metals like copper, tin and silver, commonly used in electronics, will oxidize, corrode and generally degrade, eventually causing circuits to fail.
In order to solve the problem, you will have to replace all affected parts and any parts nearby. Desolder, completely remove bad parts, clean the area thoroughly then replace with a new part.
With a piece of equipment that old, you'll probably want to go through the whole thing, searching out plague and replacing everything.
Look for green corrosion in copper. You'll see reddish brown corrosion in copper/silver components. Tin/solder will turn dull, powdery gray. Other metals will have characteristics of corrosion, depending on what they are made of. (e.g. Iron and steel will rust.)
Tin-lead solder joints can simply be reheated with a soldering iron. If it's an entire board, you might be able to bake it in an oven at about 380-400º F. then let it air cool to room temperature. If you do that, be super careful that you don't accidentally knock parts out of place when the solder melts.
If you do any soldering on the board, whether you are replacing a part or just reworking solder joints, DO NOT use lead-free solder! No! Don't even use a soldering iron that has been used for lead-free solder! If lead based solder and lead-free solder mix, even in the tiniest amounts, the solder joint WILL eventually fail again! 100% chance!
Tin is a metal that can have different oxidation states (allotropes) which behave differently. When tin oxidizes, it can form an unstable allotrope that crumbles and turns to dust. Once the process begins, it is unstoppable. The only solution is to remove and replace any oxidized tin as well as any nearby. The lead in traditional solder is supposed to stop (or slow down) the oxidation process. Without the proper mixture of tin and lead, solder will degrade. In lead-free solder alloys (e.g. SAC-305) the lead has been replaced by small amounts of copper and silver which are supposed to do the same thing. I'm sorry but I'm not a fan of lead-free. If any lead-free solder gets into standard tin-lead joints, it throws off the balance and lets the tin degrade.
Tin can also form dendrites (a.k.a. "Tin Whiskers") that grow and can potentially cause shorts. You'll probably need to use a magnifier or a microscope to see them but, if you do, they'll need to be addressed. Cleaning and reheating the solder usually fixes this problem.
Things that other people have said, above, are true. Capacitors do degrade. Transistors and integrated circuits often fail with age. Clean, check, test and replace bad components as per standard practice.
Although I don't think that your projector is bad (or has gone bad) I have a feeling like you might have to rework the entire circuit board in order to get it working the way you want. It's not an insurmountable task but I'd say that you probably have your work cut out for you.
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Like the crud inside of this stacked dual "expose switch" on a Canon 50D where you press it half way down to turn on the camera to make settings, then all the way down to take the pix, and the camera refuses to do so. Obviously this happens from some one's sweat, or just from being in a very humid location over the years getting inside on the plating. I treat them with deoxit so hopefully this common problem doesn't reappear. All the other switches in these cameras are gold plated...Comment
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Flex circuits are so much fun to rework, aren't they?
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They aren't too bad in DSLR cameras. I use a pin puller to remove them, and a puller and tweezers to deal with putting them back. They use the type of sockets that have the little flipper to unlock or lock the flat cable in place. But the amount of times you can unplug and re-plug them is limited, although I haven't discovered that exact number of times yet. For Canon It's easy to get replacement cables, as they'll sell parts to almost anyone. No camera repair tech will even work on any Nikon Digital because they are the exact opposite of everyone else. They won't sell parts to anyone. You have to salvage parts from another camera to fix a bad one. Back in the late 70's and early 80's when I worked for Canon, they had flex circuit boards in all the A series cameras. When a micro 24 or 30 pin CPU, or equivalent memory chip failed, we had to replace the bad chips while the flex board was still in the camera. It wasn't all that easy at first, but after 4 or 5 of them it became a lot easier. Part of the issue was we had to do it with a micro tip soldering iron, not a hot air gun.Originally posted by Randy Stankey View PostFlex circuits are so much fun to rework, aren't they?
The picture is just the bottom of a 7D, showing the flash and motor driver board. It also gets it's juice from a voltage regulator board on the top left of the camera. I'd bet in a 7D, there are at least 30 tiny flex boards connecting the various PCB's together. Some no more than an inch and a half long.Comment
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