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Old 2nd September 2004, 07:42 AM   #1
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Default Transformer experts needed

Hello,

Following a previous post about replacing the power transformer of a Phonic mixing desk. I have made some progress but...

Basically I have worked out the schematics, and the power supply section provides -12V, 0V and +12 V

Therefore I bought a 2* 15 V replacement transformer .

My problem is : on the original transformer there are two outputs (which I bielive are 15V each) but there is also a ground (black) wire which is at the center..

the original transformer looks like this:

----- Red (15V?)
-----

----- Black OV ????

----- Blue (-15V?)
-----


Therefore I have 5 outputs but the transformer i bought has only 4 outputs (2 coils at the secondary)

I'm really puzzle about this black wire... what should I do ? this wire is connected to the general 0V ground (chassis).

Btw there is almost zero ohm between this black wire and any of the blue wires but infinity with the red wires (but the secondary of this transformer could be bad)

Did I buy the wrong transformer ?



thanks for your help

Nano
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Old 2nd September 2004, 09:28 AM   #2
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Join Date: Jul 2003
Location: Newcastle, Australia
I would suspect the black wire is a centre tap for the blue secondary, possibly 15-0-15V. The red wires are probably a separate winding for another supply, possibly to supply higher current for lights/leds or higher voltage for phantom supply.

Have you traced out the circuitry around where the transformer wires connect to the board, and can possibly post a drawing of it?

Cheers
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Old 3rd September 2004, 05:38 AM   #3
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Join Date: Dec 2003
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Hi,

Thanks for your help.

I have started drawing the schematics.. I will scan them and post them on this thread.

Cheers

Nano
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Old 6th September 2004, 06:58 AM   #4
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Hi ,

the black wire was indeed a center tap for the blue winding. And the Red was another 12V winding. The mixing desk is now working great.

Thanks for your help

nano.
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Old 6th September 2004, 09:47 AM   #5
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Location: Newcastle, Australia
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