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Old 9th May 2012, 01:25 PM   #1
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Default Sony Transformer output

Hi everyone just found this transformer when cleaning out my working area

now i remember this came from an old sony amp, but that's it.

i did try to measure the voltage between the red and the black wires but it gave about 2volts and then quickly dropped to zero.

i'd like to know how to measure the voltage output.

so i know if i can use it with the diy amp kit i just ordered from ebay.

2x 85W TDA7294 BTL+Speakers protected Amplifier board | eBay

any help would be very much appreciated.

I also found the original PCB and when i connected the transformer the thing came to life!

anyway i measured the blue wires and they give a steady 8volts

but still no luck on the red wires


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Last edited by mrneedle; 9th May 2012 at 03:05 PM.
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Old 10th May 2012, 06:40 PM   #2
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Stray capacitance between windings inside a transformer can cause false voltage readings between seemingly unconnected leads. Use the ohm function to identify the windings. There may also be a shield that just needs to be connected to ground.
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Old 11th May 2012, 03:10 PM   #3
macboy is offline macboy  Canada
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Did you try to measure the transformer voltage with your meter in DC mode? If so, even a high AC voltage will measure as zero, since the average voltage is actually zero! This is a mistake all of us has made at one time or another. Another common mistake is measuring DC on AC range; the AC coupling cap in the meter blocks the DC and you get a zero or near zero reading (with a good true RMS meter you can measure ripple on a DC supply this way).

Another possibility is that you tried to measure across two different windings. If I had to guess, I would think that the red-black-red is a center tapped winding, and the blue-blue is another winding, probably for either a low-voltage supply (5 VDC etc) or for a VFD display, very common in Sony gear. If it's for VFD, it will be around (very roughly) 20 VAC and not capable of much current at all. As Loudthud suggested, remove power and measure resistance between wires to determine which are grouped together as a winding (low R) or are form other windings (high R).
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Old 12th May 2012, 01:37 PM   #4
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thanx for both of your reply's

but i guess there is a small language problem here and my noobishness doesn't help either.

anyway can't i just measure the voltage over the capacitor?

i did this and it gives me 40.4 volts. sounds plausible to me.... am i right?
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