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Sony TA-AX235 Protection

Discussion in 'Troubleshooting and Repair' started by wierdguy, Oct 9, 2013.

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  1. wierdguy

    wierdguy

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    Oct 9, 2013
    Hello,
    It's my first time on electronicspoint, so I'm not sure that I am posting where I should be. Nonetheless, here goes:

    I have a Sony TA-AX235. I opened it up a few days ago in order to clean the pots and change the thermal paste between the amplifier and the radiator. I cleaned the pots and switches with contact cleaner, let it sit for about an hour, in order for the cleaner to evaporate and then assembled it back and plugged it in. It worked, no more crackling switches and such...

    The next day, when I powered it on, instead of waiting a few seconds, and then starting, the relay kept closing and opening back almost instantaneously. I'm not very good with electronics. It's my fist time trying to fix something as complicated as this.

    I checked that the +/-35V and +/-12V values are correct, that the rectifier diodes are working, redid some solder joints that I thought might have disconnected whilst handling. What I found was that that the voltage on pins 10 and 13 of the power IC, instead of being close to 0V, were at about -22.7V and I'm kind of stuck at this point. I have no idea on what should be done further.

    So, in other words, I am requesting some help.

    Link to the service manual: http://freeservicemanuals.info/servi.../Sony/ta-ax230.

    Thank You!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I wonder if there was any insulating material between the device and the heatsink that you removed and failed to replace.

    (and why would you bother to open it to change the thermal paste?)
     
  3. wierdguy

    wierdguy

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    Oct 9, 2013
    There wasn't any. Either way, it is irrelevant, because the chassis links to ground, and so does the heatsink.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    What sort of contact cleaner did you use?

    Did any spill on the board?

    Is it possible that any flexible connectors or cables were left disconnected or were reconnected incorrectly, or have become pinched in something during reassembly?

    By the way, your link to the service manual is broken.

    The heatsink and the chassis may be earthed, my question was to do with the device that's mounted to it. If (as you say) there was no insulation, then the question should be moot.
     
  5. wierdguy

    wierdguy

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    Oct 9, 2013
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I would be carefully inspecting the solder connections on the pins of the output IC. It's easy to fracture the solder connections when you're screwing the IC onto the heatsink. Especially if it's a single-sided board. If in doubt, resolder them all - suck the old solder off first and don't use more than you need, but do it after all the mechanical things have been done.
     
  7. wierdguy

    wierdguy

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    Oct 9, 2013
    Alredy did that.
     
  8. shrtrnd

    shrtrnd

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    Jan 15, 2010
    This may not help, but some of those contact cleaners, especially when blown into
    pots, won't dry in an hour. Some also melt some types of plastics. Something may
    have been damaged when you powered it back up. Did you use the contact cleaner
    on switches or other components not previously mentioned?
     
  9. wierdguy

    wierdguy

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    Oct 9, 2013
    I don't recall doing so, but I guess some of it might have been accidentally sprayed on other components:-?
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Why don't you tell us what else you already did?
     
  11. wierdguy

    wierdguy

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    Oct 9, 2013
    I already did that too, if you carefully read the first post. I am really interested if anyone could give me an answer to my question, as opposed to presumptions.
     
  12. davenn

    davenn Moderator

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    Sep 5, 2009
    presumptions and guesses is all we can do when presented with limited info and dont have the unit in front of us to inspect.
    How about posting some sharp and well lit pics of the insides of the unit .... annotate the pics showing us what voltages you have measured where, where you squirted cleaner etc
    it may help us to help you

    Dave
     
  13. wierdguy

    wierdguy

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    Oct 9, 2013
    Sure will. As soon as I get home I'll take some and post them. I can't guarantee quality photos, but I'll try my best
     
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