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Old 14th September 2009, 09:55 AM   #1
pra3718 is offline pra3718  India
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Default transformer meltdown

I have 18-0-18 transformer and power to my LM3886 P2P amp. Prior to Lm3886 P2P I was using this for tda2050 mono. This transformer I was using from last one month and everything was fine. This time I decided to build TDA2050 multichannel amp. (Picture attached) First, I build single channel & test again everything was fine clear tone, no hum, no distortion etc., then I build another three channel & tested I found lot-off distortion & found IC becomes very hot. And I use white-grease then I found distortion becomes low but not clear tone. AND SUDDEN MY TRANSFORMER STARTS SMOKE. I SWITCH-OFF POWER SUPPLY AND FOUND IT WAS VERY VERY HOT & MELTING.

What is my mistake. Please help me. Attached pictures are not very clear SORRY.
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File Type: gif tda2050T.GIF (90.7 KB, 321 views)
File Type: gif tda2050P.GIF (105.4 KB, 302 views)
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Old 14th September 2009, 10:12 AM   #2
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My guesses are one of the three channels had a bad chip/was miswired or in the process of adding the three channels you somehow shorted the rails. Clearer pictures would help diagnosis.

Your transformer is dead - most likely an effect rather than a cause of your problem rather than the cause. Replace it.

Test each channel individually when you get another transformer. You might want to use a 100R 1/4W resistor in each rail to act as a current limiter (and really slow blow fuse) when you first bring the channel up. Once you are sure that the channel is basically OK, remove the resistor for further testing
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Old 14th September 2009, 11:00 AM   #3
pra3718 is offline pra3718  India
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This may help but still not very clear.
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Old 14th September 2009, 12:07 PM   #4
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Use a light bulb tester when building or changing amps. It would have prevented the transformer from self destructing.
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Old 14th September 2009, 12:19 PM   #5
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Quote:
Originally Posted by Redshift187 View Post
Use a light bulb tester when building or changing amps. It would have prevented the transformer from self destructing.
Or secondary fuses! Besides melting the traffo you could cause the bridge to explode too, neither are things you want happening. Fuses are cheap, traffos are not.
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Old 14th September 2009, 12:40 PM   #6
pra3718 is offline pra3718  India
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Thank you, can you advise how to and where to connect fuses in simply-way. i.e. After rectifier & caps and before amp. One fuse for (+) & another for (-) Is that right ?
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Old 14th September 2009, 01:26 PM   #7
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Fuses in the primary to the transformer and fuses from the secondary winding to the rectifiers is the safe approach.
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Old 14th September 2009, 02:03 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Redshift187 View Post
Use a light bulb tester when building or changing amps. It would have prevented the transformer from self destructing.
ALWAYS use the bulb tester for every new project and for EVERY modification of an existing project.
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Old 15th September 2009, 09:53 AM   #9
pra3718 is offline pra3718  India
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Infact, my plan was to build all amp on single pcb with power supply. Yes, I checked amp one-by-one. 3rd one is heating the transformer. I checked carefully I did not find any prob in wiring. Anyway, Today's lesson : Never build multichannel on single pcb.
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Old 18th September 2009, 09:56 AM   #10
akis is offline akis  United Kingdom
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Is the heatsink shorting out those chips?
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