SA-8100 protection circuit issue

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

  1. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    so pin 3 is now positive 31v ?
     
  2. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Yes, that is correct.
     
  3. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    looks like the problem ls around q1 q3 then .
     
    Last edited: Jul 16, 2017
  4. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Thanks Pete, that is interesting, since those are the new ones I put in. Would you suggest I replace them? Is it possible the 992s I put in there are not exact replacements for the 726?
     
  5. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    its possible they are fitted incorrectly . double check them
     
  6. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    2sa726 ECB
    2sa992 BCE
    so they should be turned 180 degrees to match pinouts .
     
  7. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    No, they are in correct. I followed the data sheet and the marks on the board when I put them in. They are 180 degrees from how the 726s were.

    At this point I may just put the 726s back in to see if I can get back to where I started. I checked them with the diode setting on my digital multimeter and they all gave the same signals base to emitter and base to collector, base negative and the other two positive.
     
  8. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    voltage readings q1 q3 BCE would be good to see . all reference chassis ground .
     
    Last edited: Jul 16, 2017
  9. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    OK, here are the readings:

    B C E
    Q1 -3.2 -17 -2.3
    Q3 +7.2 -41 -1.4
     
  10. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    what voltages are at each side of r13 ?
     
  11. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    On the brown band end I have 12.8 V, on the gold band end I have -1.5 V.
     
  12. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    see if it still measures in spec at 120k
     
  13. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    It started out low at about 80k, but drifted up, quickly at first then slowed down. After about 2 minutes of measurement it had drifted up to about 104k, and was slowly climbing.
     
  14. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    did you first remove one leg before testing ? if not i suggest to do that .
     
  15. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    did you reconnect q5 base ?
     
  16. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    also try pre main disconnected and see if q1 base voltage drops . if so check dc offset again .
    looks you will need to move the switch to separated and remove jumpers if present
     
    Last edited: Jul 16, 2017
  17. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    I had not removed one leg of the resistor before testing. Will do that. I had not re-connected Q5 base, should I do that?

    All of the tests have had pre-out/power in separated.
     
  18. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    After disconnecting one leg, R13 is reading 119k.
     
  19. KeithD

    KeithD Active Member

    Messages:
    269
    Location:
    La Crosse, WI
    Reconnected Q5 base and R13 leg. Measured voltage on either side of R13, brown band side +12.8V, gold band side -2.5V
     
  20. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    try slowly turning vr1 whilst monitoring pin 3 voltage and see if you can get it shift towards 0v .
    if it wont shift list all board pins voltages including grounds . as any voltage on grounds isnt good .
     

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