Hi,
I explained "my story" to David Geren, Vice President of Cinemag.
(What a great support service they offer ! :thumb: :thumb: :thumb: )
Here is his answer :
Dear Edouard;
I am sorry to hear that your “smoke test” did actually smoke. In all probability, when the amplifier died, the output transistor going to your +15V rail fused to form a direct short which passed all of the current your power supply could deliver through the transformer limited by the transformer’s dc resistance. That would have magnetized the core.
A magnetized transformer core exhibits increased THD. Also, being magnetized, its maximum output level will be significantly reduced. If you have the proper test equipment, you could do a low frequency THD test to determine how badly magnetized it really is if you have another known good transformer to compare it with.
Theoretically, you could demagnetize it by passing a high enough signal level through it. Next you would run the signal up to a level which is high enough to overcome the magnetization and then reduce the signal level. The frequency that it would be done at, by the way, is not an issue so long as it is within the band that the transformer will react to. However, you probably will require a power amplifier capable of delivering the signal at a high enough ac voltage to do the job. After doing that, you would have to test the transformer for THD to assure that the job has been properly done. This is a lot of work and the chance of returning the transformer to original specifications probably is not good.
The bulk tape eraser idea, again, is theoretically good. . . but it will not work. You probably will not be able to generate an intense enough field to do the job.
The best way to save the laminations is to bring it to a temperature to above the Curie Point (Mme. Curie was a French scientist who was, along with her husband, very important in early work on the nature of the atom). Above this critical temperature, the core no longer can support a magnetic field. This requires a furnace running at over 1000 degrees F. Again, the transformer would not like the environment.
Consider the transformer to be "dead." If you send it to us, I can test it for you. First, I must point out that a new CMOQ-2S is currently selling for $26.83 + shipping. Knowing that yours probably is badly magnetized and factoring in the value of your time, I suggest that you simply order a replacement.
With future experiments, I have one piece of advice which I have personally learned the hard way and which you now know: Check out stages in circuits de-coupled from each other. Next test them for function. Finally, hook them all together to verify that the whole system works.
Best regards,
David
