Resistor gets too hot

Discussion in 'General Electronics Chat' started by Bigbizkit, Sep 14, 2016.

  1. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
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    1
    Hi guys...
    I have this old amplifier kit from like 5years ago. The IC is broken so I replaced it. Its a Toshiba TA8205ah.
    Somehow i managed to make it work. Monitored the IC temp, gets hot fast but i think the heatsink can handle it.
    I powered it with a 12v 3A regulated power supply.
    But after a minute i smell something, and then i noticed that the 10 Ohms 1/2W resistor gets extremely hot. That its color is almost brown already.
    What could possibly be the problem? Somebody help plssss....
    The image below is the output pin of 8205ah.

    PicsArt_09-14-11.25.04.jpg
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Why do you use 10 Ohms resistors when the datasheet say 2.2 Ohm resistors?
    Also why do you have 2 X 22 Ohms resistor in the speaker lines?
    The amplifier has an high load wich might give problems.

    Bertus

    BTW the datasheet you posted is for the TA8233 and not the TA8205.
    I have attached the correct datasheet.
     
  3. DGElder

    Member

    Apr 3, 2016
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    The capacitor is 224 of what? And what do the 22 ohm resistors accomplish?
     
    Last edited: Sep 14, 2016
  4. crutschow

    Expert

    Mar 14, 2008
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    Sounds like the amplifier may be oscillating.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    224 ...220nf Mylar caps and not 22 ohm....0.22 ohm. Might be to protect amp in case of faulty speaker low Z since amp is bridged.
    I second oscillation
     
    Last edited: Sep 14, 2016
  6. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
    44
    1
    I bought it as a Kit sir.

    I bought it as a kit sir.
    Uhm so what do you think i should do sir?
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Do you a have scope?
     
  8. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
    44
    1
    No sir i dont. All i fave is a VOM testertester.
     
  9. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
    44
    1
    What should i do sir?
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    A scope can check if AMP is oscillating.
    With a VOM there is not much you can do....but you can check the electrolytic caps for leaks if you know how to.
    If you don't next option is to replace all the electrolytic caps, since from the pic I see that things is OLD.
     
  11. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
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    Ukie! Yes sir! Ill do that! Thank you!
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    waita minute....A KIT ?
    Did the KIT came assembled ?
    or did you solder all the parts on the PCB urself ?
     
  13. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
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    Nope. I bought it that way.
     
  14. R!f@@

    AAC Fanatic!

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    Assembled ?
     
  15. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
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    Yup its assembled when i bought it.
     
  16. DGElder

    Member

    Apr 3, 2016
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    I see there are 4 caps and 4 resistors circled? Are those all the R and C components in those two networks. Or are there 4 resistors for each RC network? I ask because ( assuming your schematic notes the single component values and not the network equivalent) 2 caps in series and 4 resistors in parallel would match the recomended RC values for each network. If only one network is getting hot that would provide a big clue as to where the fault lies - probably in those cap/s.

    The R/C values are important for proper phase shifting to prevent oscillations. A fault in that network could cause oscillation as well as overload of the resistor.
     
    Last edited: Sep 14, 2016
  17. Bigbizkit

    Thread Starter Member

    Oct 29, 2015
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    My schematic only shows 1channel. 1cap in series with resistor for every output of IC. (Pin 11,12 and pin 15,16)
    So there are four rresistors and 4caps.
     
  18. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The test circuit shows 0.12μF capacitors with 2.2 Ohm resistors:

    TA8205AH_test_circuit.png

    You are using 0.22 μF and 10 Ohms.

    Bertus
     
  19. DGElder

    Member

    Apr 3, 2016
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    Sorry, I wasn't paying attention. Then the values are quite different from the recommended values - giving 5x the resistance and 1/2 the reactance, so I would look at them with suspicion. There will be interplay between the choice of C2 (47uf recommended) and these 4 RC networks.

    The other thing is the confusion over datasheets and part numbers. Did you replace the IC with the exact same part and if not what are the differences in specs and recommended parts?

    In any case if it worked when you bought it and it doesn't now, then I guess it's hunt peck and swap till you find a faulty part. Not having a scope limits what you can do. Good luck.
     
    Last edited: Sep 14, 2016
  20. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I wonder why people sell kits with components that are completely different from manufacturers data sheets.
     
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