transformer meltdown

pra3718 · 14th September 2009, 09:55 AM

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.

BobEllis · 14th September 2009, 10:12 AM

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

pra3718 · 14th September 2009, 11:00 AM

This may help but still not very clear.

Redshift187 · 14th September 2009, 12:07 PM

Use a light bulb tester when building or changing amps. It would have prevented the transformer from self destructing.

5th element · 14th September 2009, 12:19 PM

Quote:

Originally Posted by Redshift187

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.

pra3718 · 14th September 2009, 12:40 PM

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 ?

jean-paul · 14th September 2009, 01:26 PM

Fuses in the primary to the transformer and fuses from the secondary winding to the rectifiers is the safe approach.

AndrewT · 14th September 2009, 02:03 PM

Quote:

Originally Posted by Redshift187

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.

pra3718 · 15th September 2009, 09:53 AM

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.
Thanks.

akis · 18th September 2009, 09:56 AM

Is the heatsink shorting out those chips?

14th September 2009, 12:07 PM	#4
Redshift187 diyAudio Member Join Date: Aug 2008	Use a light bulb tester when building or changing amps. It would have prevented the transformer from self destructing. __________________ Tyler

14th September 2009, 01:26 PM	#7
jean-paul diyAudio Moderator Emeritus Join Date: Sep 2002 Location: The Netherlands	Fuses in the primary to the transformer and fuses from the secondary winding to the rectifiers is the safe approach. __________________ It's only audio

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14th September 2009, 10:12 AM	#2
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	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

14th September 2009, 12:40 PM	#6
pra3718 diyAudio Member Join Date: Jan 2009	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 ?

15th September 2009, 09:53 AM	#9
pra3718 diyAudio Member Join Date: Jan 2009	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. Thanks.

18th September 2009, 09:56 AM	#10
akis diyAudio Member Join Date: Jul 2008	Is the heatsink shorting out those chips?

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