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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

Title: B+ and ground reversed on Neve 1064
Post by: 22busy 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.
Title: Re: B+ and ground reversed on Neve 1064
Post by: Dave Hecht 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
Title: Re: B+ and ground reversed on Neve 1064
Post by: amorris 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.
Title: Re: B+ and ground reversed on Neve 1064
Post by: 22busy 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 . . .


Title: Re: B+ and ground reversed on Neve 1064
Post by: David Kulka 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?
Title: Re: B+ and ground reversed on Neve 1064
Post by: Dave Hecht 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
Title: Re: B+ and ground reversed on Neve 1064
Post by: 22busy 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.
Title: Re: B+ and ground reversed on Neve 1064
Post by: Dave Hecht 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