SA-8100 protection circuit issue

Discussion in 'Pioneer Audio' started by KeithD, Jul 2, 2017.

  1. QSilver

    QSilver Super Member

    Messages:
    1,079
    Good news! Out of interest, where were the bad joints? Fingers crossed, you've got it. :thumbsup:
     
  2. KeithD

    KeithD Active Member

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    228
    Location:
    La Crosse, WI
    Q9 either B or E hole was not completely covered with solder. A couple of the resistor solder pads on that side of the power amp did not look the best, so I re-flowed those also. Sorry, did not make a note of which ones I re-did, but I think that was it. Everything else looked ok on the foil side.

    I think after all the tests on the protection circuit, it came down to a spike in the signal from the power amp when the unit went into protection. Since I had already replaced the 726 and 1451 transistors on there, i figured I might as well order the parts and replace all the electrolytics on the power amp. I never did see a bad transistor using the scope on the power amp. While I was at it, I ordered and replaced the NTE123AP transistors on the protection board that I put in for Q3 & 4. Bought the 945s you recommended from Mouser.

    If the recap does not solve the problem, I'm at a loss on this one.
     
  3. petehall347

    petehall347 the brandy coffee man

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    Location:
    uk.. the middle bit
    well done so far
     
  4. QSilver

    QSilver Super Member

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    1,079
    That should be it now. It shouldn't be any trouble now with protection but if it is.... please say, for curiosity's sake.
     
  5. KeithD

    KeithD Active Member

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    228
    Location:
    La Crosse, WI
    Had the amp on playing music last night and today for about 30 minutes each and no protection issue. However, I have the amp on now playing a CD and protection tripped for about 1 second after about 5 minutes of play. There does seem to be some initial static on the right channel in the first 15 seconds or so that fades away. Will just have to do more testing to see if things improve... Will report back on how it goes.
     
  6. petehall347

    petehall347 the brandy coffee man

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    Location:
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    i would swap left and right output transistors . one might be failing under load
     
  7. KeithD

    KeithD Active Member

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    228
    Location:
    La Crosse, WI
    Which ones are you calling the output transistors?
     
  8. petehall347

    petehall347 the brandy coffee man

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    Location:
    uk.. the middle bit
    the main outputs on the heat sink .q15 q17 ...q16 q18 .
     
  9. inductor

    inductor Super Member

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    Location:
    uk
    come on it cant be that difficult to fix ?, have you measured the o\p from the 2 power amps before the relay when it trips the protection ? from an early post i see the o\p goes to 0v when protect kicks in, so fault is somewhere other than the power amp,
     
    Last edited: Sep 8, 2017
  10. KeithD

    KeithD Active Member

    Messages:
    228
    Location:
    La Crosse, WI
    After fits and odd happenings, things have settled down. Playing very smoothly without dropping into protection the last couple of days. No background hiss or static (I've been noticing that on other amps lately). Just hoping this continues. It's a wonderful amp and the sound is fantastic to my ears when all is working well.
     

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