Hello, can anyone please help me locate the problem in the attached PCB? It is producing low sound and in some PCBs are no sound at all and TDA 7056B is heating up fast. Thanks for your help

 

Assuming that the TDA7056B is connected in the same way as the example on the datasheet AND the supply volltage to it is not too high then it is almost certain that the TDA 7056B needs replacing. If the TDA 7056B is good then with the speaker not connected then both output pins should read almost the same voltage with respect to ground and it should be about half the supply voltage to the chip.

Les.

 

Assuming that the TDA7056B is connected in the same way as the example on the datasheet AND the supply volltage to it is not too high then it is almost certain that the TDA 7056B needs replacing. If the TDA 7056B is good then with the speaker not connected then both output pins should read almost the same voltage with respect to ground and it should be about half the supply voltage to the chip.

Les.

Hi Sir Les,
Thank you so much for your reply. I am getting 5.4 Vdc on both outputs with respect to ground without the speaker connected to it

 

As I don't know the supply voltage to the TDA7056B on your board I don't know if 5.4 volts is about half the supply voltage. The fact that both output pins are at the same voltage suggests that there are no short circuit transistors in the output stages of the TDA7056B.
Does the IC still get very hot with the speaker disconnected ?
Does the voltage on pin 5 vary between about 0 and +2 volts as the volume setting is changed ?
Is the DC level on pin 3 about the same on a working board and the faulty one ?
Can you post a schematic of the board or at least trace out the schematic around the TDA7056B ?
Does replacing the TDA7056B fix the problem ?

Les.

 

As I don't know the supply voltage to the TDA7056B on your board I don't know if 5.4 volts is about half the supply voltage. The fact that both output pins are at the same voltage suggests that there are no short circuit transistors in the output stages of the TDA7056B.
Does the IC still get very hot with the speaker disconnected ?
Does the voltage on pin 5 vary between about 0 and +2 volts as the volume setting is changed ?
Is the DC level on pin 3 about the same on a working board and the faulty one ?
Can you post a schematic of the board or at least trace out the schematic around the TDA7056B ?
Does replacing the TDA7056B fix the problem ?

Les.

"Does the IC still get very hot with the speaker disconnected ?"
☆☆ Hi Sir, I am going to observe if the IC still gets very hot when the speaker disconnected (I will keep you informed?


Does the voltage on pin 5 vary between about 0 and +2 volts as the volume setting is changed ?
☆☆ There is no volume control that I can adjust, I am not sure of the purpose of trimpot (blue color) in pcb

Can you post a schematic of the board or at least trace out the schematic around the TDA7056B ?
Does replacing the TDA7056B fix the problem ?
☆☆ I will try to trace out schematic around TDA7056B
☆☆ The PCB is double layer and I am having problem desoldering TDA7056B.. is it okay to piggyback it (for testing purposes) with the new TDA7056B?

Thank you Sir

 

Do you not have the complete unit that the PCB is part of ? If you do then there must be some way to adjust the volume.
DO NOT try to piggyback a new IC on top of the original one. You could make a special bit for your solering iron that will heat all 9 pins at the same time. I suggest using a piece of 3mm thick copper. If you are prepared to sacrifice the coat od an IC then snip though the IC leads leaving enough length to solder wires to them. Then build a test circuit on veroboard using information from the datasheet. Test it monitoring the current it draws and see how it behaves buy injecting a signal into it's input and looking at the output on an oscilloscope. Some background information about what this board is part and your responsibility for repaiing them may be helpful be helpfull.

Les.

 

There's a blob of solder looks like it's shorting pins 5&6 together, ( pin 5 is volume control and pin 6 is speaker output).

 

There's a blob of solder looks like it's shorting pins 5&6 together, ( pin 5 is volume control and pin 6 is speaker output).

View attachment 321345

Thank you Sir, I am going to check the blob of solder when I get back to work

 

As I don't know the supply voltage to the TDA7056B on your board I don't know if 5.4 volts is about half the supply voltage. The fact that both output pins are at the same voltage suggests that there are no short circuit transistors in the output stages of the TDA7056B.
Does the IC still get very hot with the speaker disconnected ?
Does the voltage on pin 5 vary between about 0 and +2 volts as the volume setting is changed ?
Is the DC level on pin 3 about the same on a working board and the faulty one ?
Can you post a schematic of the board or at least trace out the schematic around the TDA7056B ?
Does replacing the TDA7056B fix the problem ?

Les.

Hi Sir Les, sorry for the delay. Attached is the schematic around the TDA7056B

 

Do you not have the complete unit that the PCB is part of ? If you do then there must be some way to adjust the volume.
DO NOT try to piggyback a new IC on top of the original one. You could make a special bit for your solering iron that will heat all 9 pins at the same time. I suggest using a piece of 3mm thick copper. If you are prepared to sacrifice the coat od an IC then snip though the IC leads leaving enough length to solder wires to them. Then build a test circuit on veroboard using information from the datasheet. Test it monitoring the current it draws and see how it behaves buy injecting a signal into it's input and looking at the output on an oscilloscope. Some background information about what this board is part and your responsibility for repaiing them may be helpful be helpfull.

Les.

Hi Sir Les, the volume control is adjusted via trimpot which is connected to Pin #5 of TDA7056B

 

Your schematic does not show any power supply to the circuit. The trimpot will not adjust the volume of the output as you only have the ends of the track connected. You need to have the slider connected as shown in Figs 14 and 15 on page 10 of the datasheet for the TDA7056B.
Les.