kienlen Posted January 6, 2009 Share Posted January 6, 2009 Hi, I've got an old pair of La Scalas and one of the tweeters is acting odd. It isn't completely dead, but the sound is so soft that you need to put your ear up against it in order to detect that it is producing any sound at all. They appear to be the K-77M with square magnets (although the "M" isn't printed on them at all). I have disassembled the tweeters. The diaphram appears normal to the naked eye, but I admit I don't know what a "bad" diaphram would look like. Resistance across it a touch over 6 ohms. Anyone have a clue what's going on? Thanks, Stu Quote Link to comment Share on other sites More sharing options...
kg4guy Posted January 6, 2009 Share Posted January 6, 2009 First I would take the tweeter from your other speaker and hook it up to see if is in fact the tweeter and not a crossover problem or a bad wire.If you have not upgraded your capacitors it may be a good time to do that and also replace all the wires from your crossovers to your drivers.Contact Bob Crites for crossover rebuild kits they do not cost much and are easy to install with limited soldering skills.Here is Bobs contact B&K Sound business # is 479-967-1542 or email him at bobcrites@gmail.com. Hope this helps Quote Link to comment Share on other sites More sharing options...
kienlen Posted January 10, 2009 Author Share Posted January 10, 2009 Plugging my other tweeter in seems to produce the same results. And the tweeter from the "bad" crossover sounds fine when plugged into the "good" crossover. So, I have ordered a rebuild kit from Bob Crites. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Guest David H Posted January 10, 2009 Share Posted January 10, 2009 Good call on the Crites crossover upgrade, I think you will find the instructions top notch and the parts are excellent quality. Quote Link to comment Share on other sites More sharing options...
Marvel Posted January 10, 2009 Share Posted January 10, 2009 Hopefully, you loosened and retightened all the screws on the crossover. That may have been all that was necessary. Quote Link to comment Share on other sites More sharing options...
kienlen Posted January 16, 2009 Author Share Posted January 16, 2009 Hmmm ... not having a lot of luck here. Got the new caps from Bob Crites, soldered everything in, loosened and re-tightened all the connections. The one crossover is still producing a very diminished tweeter volume. So, I double-checked everything by swapping the tweeters again and it still seems to be this one crossover. Is it possible that the 245 micro Henry inductor is bad or that the weird zener diode contraption went bad? Anyone have a way to test those parts other than swapping them out? Quote Link to comment Share on other sites More sharing options...
djk Posted January 17, 2009 Share Posted January 17, 2009 You can test the zeners by simply unhooking them. You can test the inductor by unhooking one end, and shorting out one of the 2µF caps. Quote Link to comment Share on other sites More sharing options...
kienlen Posted January 17, 2009 Author Share Posted January 17, 2009 I sent Bob Crites an email asking him the same question. He replied with the same answer as djk, above. So, this morning I'll do this and report back. Also, someone sent me a private message asking which crossovers I have, and they are Type AA, just for the record. Quote Link to comment Share on other sites More sharing options...
kienlen Posted January 17, 2009 Author Share Posted January 17, 2009 Well, when I unhook one of the zener diodes (taking care to make sure that doesn't touch it's mounting plate), everything works fine. Bob Crites mentioned that he's only seen one other zener diode go bad. Looks like I've got case number two. Couple other questions, if people don't mind ... both of my tweeters have fuses soldered into the wires from the crossover to the drivers. Is that normal, or did someone add that along the line? These are second-hand speakers that have been used in a fraternity house for something like 30 years. Is the fuse necessary since Bob Crites mentioned that the point of the zener diodes is for tweeter protection? And a somewhat obvious question ... anyone know where I can get a couple of replacement zener diodes? Thanks to all. Quote Link to comment Share on other sites More sharing options...
kg4guy Posted January 17, 2009 Share Posted January 17, 2009 Try Digi-Key they may have them. http://www.digikey.com/ Quote Link to comment Share on other sites More sharing options...
djk Posted January 18, 2009 Share Posted January 18, 2009 Obsolete part, hard to find. See if BEC will sell you some. I have a source, but they have a $50 minimum order. The speakers may be played at moderate levels without the zeners. The fuse was added by someone. A 211-2 automotive lamp works better. Quote Link to comment Share on other sites More sharing options...
JohnA Posted January 19, 2009 Share Posted January 19, 2009 I disconnected my zener soon after I got mine because I disliked their harsh, hashy sound. I've sence played the system at quite immoderate levels indoors without damage. i am obsessive about clipping, though. Quote Link to comment Share on other sites More sharing options...
kienlen Posted January 19, 2009 Author Share Posted January 19, 2009 Well, Bob Crites has these as well for $12 each. I'm just going to order them from him because he's been very responsive to all of my questions and I love giving people my business when they are very helpful. And while I'm sure they could go without the zener diodes if they had a responsible owner, I'm just going to put new ones back in. These things lead a very tough life in the fraternity house. And I don't want to have to fix these any more often than I absolutely need to. The physical condition of the cabinets would make anyone who cares enough to read this forum break down in tears. But that's part of my attraction to them. Anything that can take this much physical and electrical abuse earns my respect. Quote Link to comment Share on other sites More sharing options...
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