SA-8100 protection circuit issue

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

  1. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    OK, I am making a list for Mouser. I will order the 945s. What other components are prone to failure that I should be thinking about replacing and thus having parts on hand?

    Also, thinking about a better soldering iron. What do people recommend?

    Last, will probably order a new dmm. I was thinking about Fluke 87 V. Any suggestions/recommendations?

    Just want to say thanks so much for all the help and those who stuck with me through this whole process. I would have been completely in the dark and at the mercy of expensive repair options without this forum. Want to especially thank Pete for his help over many days!
     
  2. evoroadster

    evoroadster AK Subscriber Subscriber

    Messages:
    289
    Location:
    Honolulu, HI
    Hallelujah! Glad to see this is over and done. I recently sold my SA-8100 and sincerely hope the buyer never has to deal with something like this.
     
  3. QSilver

    QSilver Super Member

    Messages:
    1,094
    If you haven't already done so, it could be a good idea to change all the electrolytic capacitors - but you can leave it for a while if you've had enough soldering for now!

    Have you changed out the 2SC1451's, and 2SA756's in the amp?
     
  4. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    I changed out the four 2SA726 and two 2SC1451 transistors on the power amp board and the two 2SA726 transistors on the control amp board.

    By the way, Q6 on the protection board is 2SC945, same as Q3 and 4 that were having problems. I had ordered KSC2383YTA to replace Q6. Is that a better or same replacement than KSC945CGTA for Q3 & 4? I see there is another 2SC945 in the power supply unit.

    I see there are a lot of electrolytic caps in there. Is there a list of all the recommended replacement part numbers?
     
  5. QSilver

    QSilver Super Member

    Messages:
    1,094
    I think Q6 can be replaced with a KSC2383YTA successfully... The 945's in the regulators of the power supply may need to be replaced with a different transistor... a KSC2383 might work but I'd double check with someone like MTF. If you google SA-8100 and audiokarma you might find a cap and transistor list or be able to build one up.

    Usually you can change most of the capacitors with something like Nichicon PW's or Panasonic - these seem to have less leakage than Nichicons...

    Some capacitors can need to be bi-polar.. I think in the phono pre-amp section? Smaller ones like 1uF and lower you can change over to film capacitors.
     
  6. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    Update: after playing the amp for a few days, it seems the issue remains. :(

    The first time I turned on the amp after putting in the 123As, it came out of protection as it should. After a few minutes it went in and out of protection for a while. I decided to set the idle current and neutral potential following the service manual. The amp came in and out of protection a few times during this process, but eventually settled down. Each day after that it got better - dropping into protection fewer times. However, at this point it still seems to drop into protection once at around 15 minutes of play time for about 2 seconds. I'm planning to replace those 123As in Q3 & 4 with the suggested 945s, but will need to order them. Anything else that might be the culprit that I should add to my order just to have on hand??? I really hope replacing Q3 & 4 solves the issue. This is starting to get exhausting and I might have to walk away for a while if I don't solve this soon.
     
  7. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,508
    Location:
    uk.. the middle bit
    are the speakers ok ?
    try running one channel at a time and see what happens . there may or may not be a over current sense issue .
     
  8. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    I had nothing connected when I was setting the idle and neutral potential. That whole process, including letting it warm up for 10 minutes as the manual states, took about 20 minutes or so. For all the other times, I'm using the same 8 ohm KLH speakers I've been using for months with my SX 780 with no issues. I was thinking I should try running the amp again with nothing connected to see if it drops into protection on its own. That was the case way back before I replaced anything.
     
  9. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    Ok, just tested the amp with nothing connected and pre out/power in separated. Amp went into protection after 7 minutes of on time. Only lasted a second or two.

    So, this seems to still have something to do with either the power amp unit or protection unit. When I measured the voltages on all pins of the protection board previously, they were all as expected.

    It seems like when some part warms up to a certain point it discharges a voltage that trips the protection relay.
     
  10. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,508
    Location:
    uk.. the middle bit
    am wondering if something on the same power circuit like a fridge or air-con is doing it .
     
  11. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    I shouldn't think so. I've tried three different circuits, none of which has a major appliance on it.
     
  12. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    Anything specifically I could measure/monitor when it goes into protection that might give an indication of where the problem lies, or what signal is straying off to trip the protection?
     
  13. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,508
    Location:
    uk.. the middle bit
    protect circuit .
    pins 2 and 4 to see if dc offset alters .
    q7 base to see if it loses voltage .
    you could lift d5 to rule out over-current .
     
  14. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    connected pins 2 and 4 to dmm. for the first several minutes the voltage varied a lot from +12 to -15 mV. It then settled down to 1 to 2 mV. The unit went into protection after about 7 minutes but the voltage did not change.

    Measured Q7 B voltage referenced to ground. Started out at 9 V, but slowly drifted down to 8.7V over 5 minutes. Unit then when into protection and voltage dropped to 2V, then came back up after the relay came out of protection. I'm fairly certain the relay tripped before the voltage on Q7 B dropped rather than a drop in the voltage causing the relay to trip. Is that possible? Does that indicate a problem with either the relay or connections on the speaker side?
     
  15. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,508
    Location:
    uk.. the middle bit
    now monitor q6 base .
     
  16. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,508
    Location:
    uk.. the middle bit
    also be worth looking at pin 16 voltage to see if it rises or drops .
     
  17. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    Q6 B at -1.14V and steady. After protection trips it momentarily goes to +0.3, then comes back to -1.14V before protection re-engages.

    I have to let it sit/cool for a few minutes before I turn it on again to monitor pin 16. I've noticed if I just turn it off, move dmm lead and then turn it on again, it does not drop into protection, which to me indicates a temperature issue.
     
  18. QSilver

    QSilver Super Member

    Messages:
    1,094
    A scope would help here. Probe all the legs of the transistors and see if you can find any "noise" on them. Often I find that the transistor causing the problem is hurling out all sorts of noise which makes the protection circuit go in and out.
     
  19. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    I can do that, but would need instructions on how to set the scope to test each transistor.
     
  20. KeithD

    KeithD Active Member

    Messages:
    248
    Location:
    La Crosse, WI
    Is the thought here that the problem is still on the protection board itself and not the relay or something external to the board?
     

Share This Page