R/E/P Community
R/E/P => R/E/P Archives => Bruno Putzeys (Designer) - Dave Hecht (Master Tech) => Topic started by: 22busy on March 10, 2009, 12:26:35 AM
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A Neve 1064 (same basic amplifier circuit as a 1073) had the B+ and ground reversed just long enough to smell something burning. Now, with a mic connected to the module, it passes signal but it sounds thin, like it dropped one leg of a balanced connection.
I'm having difficulty troubleshooting the problem and would welcome any suggestions on things to try.
I measured the mic transformer's and output transformer's primary and secondary windings. They measured almost exactly the same as a functioning module.
Then I swapped BA283 amplifier cards with a working unit and the problem remained with the broken module.
thanks in advance.
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Just to rule them out, swap 283 & 284 cards from a known good module. Those will probably test ok. Next, check the electrolytic caps mounted in the frame - I've put one in backwards during a re-capping and they let the smoke out pretty quick if they get the wrong polarity. Also, look around for any components with burn marks.
Dave Hecht
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try blowing the cards with air, then do the smell test. at first it will all smell like smoke, but if you purge it, the component will stand out better.
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Thanks very much for the replies Dave and amorris.
Unfortunately no luck so far, but here's what I've tried. I swapped 283 and 284 cards from a working module, but no change. The electrolytics test ok with an ESR meter. With a digital multimeter none appear to be open or shorted.
Can't see any fried components and can't locate any thing by smell.
It sure sounds thin, like a dropped leg of the output transformer, but the primaries and secondaries measure almost perfect with a good resistance meter. Also, there's no low impedance path between the primaries and secondaries.
I did rule out the input transformer because the module still sounds thin with a signal coming in from the line input.
Puzzled . . .
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Even though the circumstances of the failure are a little unusual, I would just approach it like a normal troubleshooting task; power it up on the bench and check signals stage by stage with a scope. Keep in mind that there may be multiple problems. Do you have a schematic?
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Are you testing with the eq switched in or out? If the eq is in, try switching it out and just troubleshooting the amp sections first.
Davw Hecht
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David K. - thanks, been dreading dragging the o-scope and signal generator out, but it's looking like it's gonna have to happen. I'm not sure I've got a good schematic on this beast. Plus the one's I've seen are kinda hard to follow with all the edge connectors and plug-in modules.
Dave H. - good thought. I did test with eq switched out of the circuit but it made no difference.
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You can get the full 1073 manual from the AMS Neve site. As a simple test, just compare the input to the output transformer on the bad module and a known good module.
Dave Hecht