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Author Topic: B+ and ground reversed on Neve 1064  (Read 3138 times)

22busy

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B+ and ground reversed on Neve 1064
« on: March 10, 2009, 12:26:35 AM »



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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Dave Hecht

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Re: B+ and ground reversed on Neve 1064
« Reply #1 on: March 10, 2009, 02:28:16 AM »

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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amorris

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Re: B+ and ground reversed on Neve 1064
« Reply #2 on: March 10, 2009, 10:27:00 AM »

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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22busy

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Re: B+ and ground reversed on Neve 1064
« Reply #3 on: March 10, 2009, 07:01:16 PM »

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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David Kulka

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Re: B+ and ground reversed on Neve 1064
« Reply #4 on: March 11, 2009, 12:28:39 AM »

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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Dave Hecht

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Re: B+ and ground reversed on Neve 1064
« Reply #5 on: March 11, 2009, 02:20:12 AM »

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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22busy

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Re: B+ and ground reversed on Neve 1064
« Reply #6 on: March 11, 2009, 07:42:29 PM »

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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Dave Hecht

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Re: B+ and ground reversed on Neve 1064
« Reply #7 on: March 11, 2009, 09:13:50 PM »

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
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