N72 - low output problem.

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I have 8- N72s I built a few years ago. Love 'em.  
One of them is misbehaving...

The bad module is lower in overall output level than the others - about 6db.  When I use my console osc. it appears to lose more level in direct proportion to the lower the freq i send to it.  
The Neotek desk osc. is a little limited - 15k, 10,k, 3.5k, 100hz, 50hz.

Originally thinking the 6db dif. might mean a balancing issue somewhere, I visually combed the module closely several times, replacing any suspect looking soldering, but to no avail.  
Anyone have any suggestions about where the prob might be located?
Any help appreciated.

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... anyone??

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In case anyone else has a similar problem, thought I'd post this timely email response from SCA re. my original question ...

"Carefully check the input transformer jumpers and output transformer solder
joints. Poke the output transformer tape to see if the symptom comes and
goes with pressure on the windings. Verify good solder joints at the yellow
tantalum coupling capacitors.

Best regards,

Seventh Circle Audio"