heavyrocks Posted January 16, 2010 Share Posted January 16, 2010 I have come into possession of an Altec 9442A power amp. (150W stereo @ 4ohms or 300W bridged @ 8ohms) The previous owner was using it with speakers that weren't power or impedance matched. (2 Cerwin Vega V-30's - 200W @ 8ohms) I believe he was using it in stereo, not bridged mode. Both speakers still work fine but the power amp is silent. I looked inside and nothing was visibly damaged or charred. When your amp dies from poorly matched speakers, what components go first? Where should I start looking for the problem? Link to comment Share on other sites More sharing options...
Matt Pengelly Posted January 16, 2010 Share Posted January 16, 2010 Whilst it isn't the best matching in the world from the previous owner the only way it might have damaged the amp is if he was expecting more from the speakers and pushed the amp into clip too often. Eventually that could lead to problems. Was it definitely still working immediately before you bought it? As for the problem now, does the amp power on OK? If so, does it pass any sound at all before dying or is it powered up but always silent? Does the protection or clip LEDs light at any point? What speakers are you using with the amp now and how are they cabled etc? Link to comment Share on other sites More sharing options...
Sound In Gloucestershire Posted January 16, 2010 Share Posted January 16, 2010 why would an amp die from poorly matched speakers? have you tried a new fuse? Link to comment Share on other sites More sharing options...
djandydee Posted January 16, 2010 Share Posted January 16, 2010 Could be any number of things but check the fuse in the plug and the 5A fuse on the rear. If you have access to a multimeter, check the output from the mains transformer at test points +VCC and -VCC for about 28Vdc. If all these are present then it will need a more electronic based look with an osciloscope down the signal path I have attached the circuit diagram if that helps. http://www.altecpro.com/pdfs/vintage/Elect...er%20Manual.pdf Link to comment Share on other sites More sharing options...
heavyrocks Posted January 18, 2010 Author Share Posted January 18, 2010 Haven't tried a new fuse yet but will. The fuse appears to be intact though. The power LED does go on, but there is absolutely no signal coming through. A few months ago I could get one channel to work. The speakers are cabled with regular old speaker cable. I'll try swapping out speaker cables I guess. Thanks to all of you. Link to comment Share on other sites More sharing options...
heavyrocks Posted January 19, 2010 Author Share Posted January 19, 2010 Swapped the fuse. Not the fuse. Upon a closer listen the power amp is emitting a 60Hz hum like it's on. Nothing through the speakers though. The power light will stay on several seconds after being powered off. Does that eliminate any of the caps? Tested the speaker cable with a multimeter, it should be fine. Link to comment Share on other sites More sharing options...
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