SA-8100 protection circuit issue

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

  1. QSilver

    QSilver Super Member

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    1,093
    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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    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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    well done so far
     
  4. QSilver

    QSilver Super Member

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    1,093
    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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    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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    i would swap left and right output transistors . one might be failing under load
     
  7. KeithD

    KeithD Active Member

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    Which ones are you calling the output transistors?
     
  8. petehall347

    petehall347 the brandy coffee man

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    the main outputs on the heat sink .q15 q17 ...q16 q18 .
     
  9. inductor

    inductor Super Member

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    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

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    269
    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.
     
  11. KeithD

    KeithD Active Member

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    269
    Location:
    La Crosse, WI
    Still finding intermittent tripping of the protection circuit for 1 or 2 seconds after about 5 minutes of play, then good for as long as the amp is on.

    I'm thinking about the next thing I should do in terms of parts replacement. I was looking at the list on AK of transistors known to cause problems. I see the 2SC1313 is on there. One thing that is confusing is the 8100 service manual lists 2SC1345 and 2SC1313 interchangeably, and they are always listed together. One will be the transistor listed on the parts list and then underneath the other one will be listed in parentheses. Anyone know what this is about? The complete replacement list here on AK (http://www.audiokarma.org/forums/index.php?threads/sa-8100-cap-list.463178/page-2) only lists 2SC1345, there are no 2SC1313 transistors on the list anywhere. I have not opened my amp recently to determine if I have any 2SC1313 or if they are all 2SC1345. The latter is not on the list of transistors known to go bad.

    My other thought was to recap the electrolytics on the power supply board as many of these caps are large. Is that a good idea in general?

    I can live with this rather minor protection issue; however, it's more the thought that something is not right and should be fixed. Other than this issue, the amp is fantastic. Dead silent when no signal or in between songs. Sound quality is great, just love it.
     
  12. QSilver

    QSilver Super Member

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    1,093
    Yes, change the capacitors in the power supply. That board is crucial for making sure everything is and will stay stable in the amplifier. Check Q1 and Q2 for blackened tabs and heat stress and heatstress on the board around large resistors too. Check the voltages coming out too, they're all marked on the schematic which is a big help.

    Whether it helps or not, its worth it. Capacitors aren't expensive and the damage if something goes wrong would undo a lot of your hard work.
     
    Oldsansui441 likes this.
  13. KeithD

    KeithD Active Member

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    269
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    Parts came in last week and I recapped the power supply board. Presto! No falling into protection now for four days, so I believe that has solved the issue. I tested all of the old caps after taking them out. Most were testing high between 15 and 20% of original capacitance. The large one on the power supply board, C16, tested 27% high, and C12 and 13 were high by 29 and 33%. So, not sure which one specifically, but one or more were causing issues.

    I also went back and tested all the caps I took out of the power amp and protection boards. Here again, all caps were high by 10-20%. A few were over 30% high, and one was 63% high.

    Just out of curiosity, what is considered an acceptable range of capacitance to be considered "in spec"?

    I ordered replacements for all of the electrolytic caps that remain (save one that was on back order), so I can finish the recap when I have time. I agree this is totally worth it. The 8100 is such a wonderful sounding amp and versatile with all the separate controls. Can't speak more highly of it as a Pioneer product.
     
  14. petehall347

    petehall347 the brandy coffee man

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    look up the rating on the old caps . they might be plus 100 percent .
    they wont be as good as new ones anyway .
     
  15. KeithD

    KeithD Active Member

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    Wow, that seems like a lot. I thought I saw somewhere the general rule is 20%, but I could be totally mistaken.
     
  16. petehall347

    petehall347 the brandy coffee man

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    some old ones had some odd ratings
     
  17. QSilver

    QSilver Super Member

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    1,093
    I just went through an SM-700 recently and the tolerance on the caps was +100% -30%. Kinda vague! but even then, new ones will be much closer to what the schematic suggests and much less leaky etc. so they're better parts in general. I would guess that even though there is a tolerance, the actual rating ie 100uF, is the optimal specification...?
     
  18. KeithD

    KeithD Active Member

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    269
    Location:
    La Crosse, WI
    Started the rest of the recap today. Got the equalizer and control amp done. On the bottom of the control amp there are four sanyo capacitors that do not show up on the schematic. Picture is below. Anyone know anything about this? Were these added by someone later or are these stock?

    File Oct 21, 11 40 46 AM.jpeg
     
  19. petehall347

    petehall347 the brandy coffee man

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    they look original .change them they have a bad rep
     
    Oldsansui441 likes this.
  20. KeithD

    KeithD Active Member

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    269
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    Ok, not sure I've got any equivalent ones around, since they are not on the schematic. I only ordered the ones on the schematic, but I always order double, so I have extras of all the electrolytics in this amp. I'll have to look to see if something will work. Is it correct that the capacitance should match, but the voltage rating can be higher?

    On the other hand, since they are not on the service manual schematic, to they need to be in there at all?
     

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