Amp voltage problem

[guidoilieff]

Hi, I made this amp and the first time I plugged it I had the neutral/ground in the negative and vice versa.

I replaced the fuses and load with 100ohm resistors.

The light blue resistor (positive) doesn't get hot, has 40v across and remains with that voltage when I unplug the circuit.
The orange one does exactly the opposite. Gets hot, has 19v across and voltage disappear when I unplug the circuit.

The output (salida) with the 100ohm resistor gets hot and has 19v dc too and I dont think thats a good thing.

TDA doesn't get hot at all.




So, replacing the TDA will fix all this problems? They are very expensive here and I cant just order some, I need the government permission.

Bridge seems fine but I dont have an oscilloscope.
There are no shorts or open circuits. No cold solder or bad joints.

[Rob Strand]

The orange one does exactly the opposite. Gets hot, has 19v across and voltage disappear when I unplug the circuit.

The output (salida) with the 100ohm resistor gets hot and has 19v dc too and I dont think thats a good thing.

It doesn't sound like a good thing to me either.

It looks like the negative rail (pin 15) is connecting to the output (pin 14) through the IC.

What I think has happened is the output transistor on the negative rail has blown short circuit (It is normal for output transistors to blow short circuit).   If this is true  there is a good chance that -Vs (pin 15) is shorted to the output "Out" (pin 14).  The possible short is inside the chip, see "Block diagram" and output transistor "M2" on figure 15 of the datasheet:

http://st.com/resource/en/datasheet/tda7294.pdf

Remove the power and measure the resistance between pin 14 and pin 15 of the TDA7294.  If you can see a dead short (nearly 0 ohms) then it  I would strongly suspect the TDA7294 is blown.

So, replacing the TDA will fix all this problems? They are very expensive here and I cant just order some, I need the government permission.

Not good either.

[guidoilieff]

The orange one does exactly the opposite. Gets hot, has 19v across and voltage disappear when I unplug the circuit.

The output (salida) with the 100ohm resistor gets hot and has 19v dc too and I dont think thats a good thing.

It doesn't sound like a good thing to me either.

It looks like the negative rail (pin 15) is connecting to the output (pin 14) through the IC.

What I think has happened is the output transistor on the negative rail has blown short circuit (It is normal for output transistors to blow short circuit).   If this is true  there is a good chance that -Vs (pin 15) is shorted to the output "Out" (pin 14).  The possible short is inside the chip, see "Block diagram" and output transistor "M2" on figure 15 of the datasheet:

http://st.com/resource/en/datasheet/tda7294.pdf

Remove the power and measure the resistance between pin 14 and pin 15 of the TDA7294.  If you can see a dead short (nearly 0 ohms) then it  I would strongly suspect the TDA7294 is blown.

So, replacing the TDA will fix all this problems? They are very expensive here and I cant just order some, I need the government permission.

Not good either.

Holy jesuslordallmighty, almost everything is shorted

Never realized to look up for the ic schematic. I wouldn't figured it out anyway.
A zillion thanks, Ill try tomorrow with another ic, this time with resistors, not fuses.


(I think Feyman would have said the same with the problems of this amp)