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Diagram Questions

  1. Aug 20, 2012 #1
    First question is about connecting the signal inputs. If you look at pin 7 and 13 and 8 and 15 you see they are connected. I would read this to mean that the input voltages are combined with the supply voltages. This seems unusual. Am I reading it right?

    Where do I connect the actual audio inputs in this diagram? At the black dots above the pin 7 and below pin 8? Not super clear to me.

    If I'm not planning on using the mute or standby can I leave that part of the circuit out?

    The squiggly circle on the left of the diagram - what is it?

    TDA7294 Datasheet

  2. jcsd
  3. Aug 20, 2012 #2
    You are reading the schematic wrong. Pin 7 is the positive power supply for the input amplifier, Pin 13 is the positive power supply. for the output driver. They are supposed to be shorted. Neither is the input (same goes for 8 and 15, they are the negative supplies). The actual audio inputs are pins 2 and 3. That little squiggly circle with the sinewave in it is your input source.

    According to the datasheet, the mute and standby inputs are active high so just connect those pins to ground if you don't want to use those features.
  4. Aug 20, 2012 #3
  5. Aug 22, 2012 #4
    Hello gents.

    Finished my 1st effort on the TDA7294 this evening. It does not work, perhaps not surprisingly. :-)

    I'll post pictures probably later/tomorrow in an effort to get you guys to help me debug it. In the mean time I wonder if there's some way to know what part of the circuit is faulty.

    I should say that while checking the connection between 13 and 15 there was a snap/spark. I think this was due to soldering that may have been between the pins. Went up in a flash. Not sure if I cooked the IC or not.

    I have a 2A 25.2v power supply feeding it but the multimeter shows around 13.6v at the power source and at pins 13 and 15. No voltage at all between 14 and ground. Input device (MP3 player or my iPod) works fine on the 14w amplifier (TDA2030) so I doubt that's the issue. Not sure if I should check that for voltage or whatever.

    I'll throw up some pics later, as promised.

  6. Aug 22, 2012 #5
    How about the voltage on pin 8 and 15?

    Scan a copy of your schematic and take a few picture of your circuit from different angle. There is no way to troubleshoot like this.
  7. Aug 23, 2012 #6
    Despite sincere efforts from my cat I was able to get some stuff uploaded.

    Imgur Album

    The red dots indicate a soldered connection. I left the 'legs' on the caps and resistors because I was pretty sure it wasn't going to work right off. Thus it may appear that there are connections but there may not be!

    One of the 1000 uF caps has a bulgy top - not sure if this correlates 100% with a bad cap or not though.

    The reference diagram is the 'typical application' in the TDA7294 datasheet.

    Anyways, help appreciated.
  8. Aug 26, 2012 #7
    Friendly bump.
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