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Old 24th October 2004, 05:25 PM   #1
gecko is offline gecko  Argentina
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Location: Argentina
Unhappy Somebody help me!!

Hi! greetings from Argentina!
I have a little problem with a Power amp that I did,
I used This schematic for the amp
and a power supply with a transformer of 30-0-30 v ~3 A
Power transistors: MJ150015 - MJ150016
Drivers: BD139 - BD140
I wanted a power of 60 W or less, because I want to use it just
where in my room, I really don't need so much power..
I designed the pcb, and made de pcb, solded all the components
and I was ready for the test... so I connected the power suppy and..
I saw some smoke comming from the amp so I turned out quickly and found that the driver "BD139" was really hot, beside the fuse for the negative rail was blown

I'm not sure what to do now, who could help me with his?
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Old 24th October 2004, 07:48 PM   #2
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Go back and check all of your work. it is easy to make a mistake and insert a component the wrong way or accidentally draw a trace wrong etc.

You may have to look up the data sheet for all the transistors to make sure there all inserted correctly etc.

Take your time and very carefully and systematically check each and every component. Im sure with some very carefull checking you will find it....

Maybe someone else can comment about the schematic if there is an error there.



Zero
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Old 24th October 2004, 08:09 PM   #3
gecko is offline gecko  Argentina
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Thanks Zero, that's what I'm doing right now, but it could take a while..

I took some photos of the amp, here's one
Attached Images
File Type: jpg amp1.jpg (55.6 KB, 184 views)
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Old 24th October 2004, 09:06 PM   #4
jleaman is offline jleaman  Belgium
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You should never *EVER* just power on a poweramp that you just built you shold have a variac and a few meter's connected to the amp. also no speaker or line level input's should be on either.. and i was taught that shorting the center pin Positive of the input to ground helps occilation at start up..
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Old 24th October 2004, 10:17 PM   #5
gecko is offline gecko  Argentina
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Thanks Jeason, I'll take that for the next time..
I have read that I should use a variac but I didn't have one
and I was impatient to power it up
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Old 24th October 2004, 10:40 PM   #6
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Default Ola Hermano, hello brother!

Es una gran satisfaccion nuestros hermanos juntos!
That's a great satisfation see our brothers together!


haga siempre la utilizacion de resistores in serie con la alimentaccion. Use always resistors in series with the supply, you can use 100 ohms, this way, 2 volts measured over the resistance will correspond to 20mA.... and 10 Volts will result in 100mA current flowing.

This way you will protect your circuit, if damaged, or assembled with human errors, the supply voltage will be over the resistor... see that if some short happens, all the supply voltage will be over the 100 ohms resistor...and 300mA to 400mA will be flowing into the circuit halves.

That current, will not burn output transistors, maybe can destroy some small ones, but you will protect before checking again.

Always check twice the assemble, it is easy to make mistakes....i had informs from a friend that assemble one transistor inverted 6 times..... and checked many times....he burns a lot of transistors till he discovered the mistake.

Nosotros somos humanos hermano, subjetos a errores.
We are all human brother, subjected to failures.

Bienvenido hermano....Welcome brother

regards,

Carlos
__________________
Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 24th October 2004, 11:02 PM   #7
gecko is offline gecko  Argentina
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Gracias por tu ayuda Carlos
I'll try with that too, I'm still looking the circuit and checking
the components, I'm still not sure where the smoke came from..
It thought it was from the BD139 because it was really hot, but It seems to be okay, at least not o/c or s/c found

you're from brazil? that's cool!
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Old 25th October 2004, 12:34 PM   #8
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Default And you from Argentina, that' cool too.

We are very important to South America.

Argentina, as one Spanish Arm, is showing us pride and organization, courage (Malvinas) and determination, and we respect you all as a hell!.....too much respect, not a evil respect.

And we, alike ants, last years doing same job, and you have our cars in your streets, also i have one made in your country.

The South Market Cooperation, the barriers we are going to destruct together, will make our South America independent of every place, related to all subjects... we will share things, just for fun, as we are near to be completely auto-sufficient....we..... South America.....we....together...hermanos para siempre!

You can count on me, will have always more attention, as we respect you all.... do not mind for us that you are passing bad times, we have sure, and we will help you all, to be stand and strong and full or pride as always you were.

Viva la Argentina!

regards,

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 25th October 2004, 10:38 PM   #9
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I find that it is helpful to construct the circuit on a breadboard first, not as much for quality testing but mostly for DC bias. If DC bias is correct, then the circuit is correct for the most part and the chances of burning something on initial power up is reduced. If something smokes, then you can replace it much easier. Also, it is really helpful (particularly for the less experienced) to see how each componant is connected in the circuit and once you get the circuit built correctly, you can disassemble and reassemble one part at a time. Less chance for mistakes.
Of course what works for one person may not for another.
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Old 26th October 2004, 04:37 AM   #10
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After conforming that there is no wrong component at the wrong place, orientation etc. etc., check the resistance between the body of the outputs and the heatsink. Take care to cleanup the excess heatsink paste if u have used.

Checking should best be done by a second person as u will tend to make the same mistake.

Gajanan Phadte
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