SX-626 TURN ON THUMP Wrong Cap and other Questions

Discussion in 'Pioneer Audio' started by moondogtn, May 9, 2017.

  1. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Ok....so, I decided to go ahead and try to finish up this little project. All was working before I decided to go ahead and replaced the remainder of transitors on power amp board. Q1-Q8, used list I provived initially.....and during alignment noticed voltage was off (showed 24 VDC) on Q11 case. Upon further investigation, I notice 2sc2690 I had installed in Q5 was backward. I removed and installed correctly, voltage was now correct on both channels but no sound (very faint) out of right channel, actually there is sound but very faint??? I went ahead and went through alignment. VR1 and VR2 set to 28.5 which is half of my collector voltage on Q9. and Q10 respectively. I also checked dc offset and set to 17mV. Still nothing out of right side. There is some sound but very, very, faint. So, I went through and checked things again. Still am not finding anything blatantly wrong. I checked volages on Q5 and Q6 and they seem fine as well? Any ideas? I may have lost a component or???

    Bill
     
  2. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    I have been busy with school and work so haven't had much time to dedicate to this. I can post up voltages at different test points if that would help. I hope to try and connect to another receiver using preamps just to confirm issue is with power amp board. Thanks for any advice of this.

    Bill
     
  3. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    I hooked up the preamp out to another amp and all is good. So, this means something on my power amp board is causing the issue, correct? I am going to go back through and see if I can determine what is bad on that channel.
    Any thoughts on things to check as it was working prior to installation of Q1 through 8.

    Bill
     
  4. goat67

    goat67 AK Subscriber Subscriber

    Messages:
    3,851
    Location:
    Twin Cities MN
    Lets see it was working and then you installed Q1 - Q8 and it quit working.... hmm maybe something wrong with the work you did installing Q1-Q8?
    Verify each transistors pins and how they are installed. Test each one or better yet replace them again but install them correctly.

    Another thing to do is compare the voltages from the good side to the bad side to identify the bad component
     
  5. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Goat, I appreciate the suggestions and will recheck tonight but I have done all that as I am sure it had to be the last work I did or maybe a component.

    My question may have been poorly worded. What I am asking is regarding the likelihood that I lost or killed a component? Maybe when I installed Q5 with wrong orientation? Or maybe one of those loose bias wires touched something.

    I am still digging into it but just trying to figure out where to look next.

    My voltages seem comparable but I will check those again and post findings if I don't come up with a solution. Thanks again.

    Bill
     
  6. goat67

    goat67 AK Subscriber Subscriber

    Messages:
    3,851
    Location:
    Twin Cities MN
    Something is bad in the circuit. You have one channel that works. You can check each and every component one by one or you can trouble shoot this by verifying the voltages.
    Worse comes to worse swap a component one at a time between channels as a last resort.
    Lift a leg of R23 R25 R27 R29 R31 R33 and ohm these out
    Pull Q9 Q11 and test these

    So measure the voltages at each Transistor

    Q1
    E
    B
    C
     
  7. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Sorry it has been a few weeks. Death in the family and work have been keeping me busy.

    . I have taken readings on right channel which is where the issues lie. I can tell something is way off but haven't been able to figure out what it is. C6 has about 55 volts being applied to it. Below are the readings for transistors on that side. Ground is at chassis, volume turned down, no speakers connected.

    Q2
    E = .27
    B = .27
    C = 54.5

    Q4
    E = .7
    B = 1.3
    C = 27.6

    Q6
    E = 28.4
    B =29.02
    C = 55.5

    Q8
    E = .661
    B = 1.24
    C = 26.74
     
    Last edited: Aug 1, 2017
  8. goat67

    goat67 AK Subscriber Subscriber

    Messages:
    3,851
    Location:
    Twin Cities MN
    Sorry for your loss.

    The collector of Q2 should be at 33v not 54.5
    This signifies that it is not conducting something is open from here to ground. So a resistor or the transistor.

    Verify Q2 take it out of the circuit. If you do not know how to do this replace it make sure it is installed correctly. Looks to be shorted E to B or installed incorrectly.
    I would ohm out R4 R6 R8 R10 R12 lift a leg of each before measuring.

    If nothing here is bad I would then check all the other components connected to this transistor. Of interest would be C20 if it is shorted it could produce these symptoms highly unlikely though
     
  9. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    I removed and tested Q2 and it tested odd but then retested and it seemed fine...strange. I have a new one that I am going to install just to see. I confirmed the orientation is correct. I will hope that the other was just a shoddy component. I also lifted one leg and measured resistors. So far, I haven't found anything bad.
    R2=2.2K
    R4=2.2M
    R6=101K
    R8=18K
    R10=14.89K
    R12=146
    R42=100K

    I will post up outcome shortly..

    Bill
     
  10. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Soldered everything back and now we are good! I assume it was just a faulty component as it tested funny both on my meter and in my component tester.
    I am undecided about digging into the stereo lamp again or just leave it alone. I need some sleep as the heat down here in TX has been brutal. Goat, thanks for the help. I will keep this thread updated.

    Bill
     
  11. goat67

    goat67 AK Subscriber Subscriber

    Messages:
    3,851
    Location:
    Twin Cities MN
    Glad I could be of some help
     
  12. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    I haven't used this much since completion and tested it with small speakers I never noticed but there is a NASTY turn on thump. I replaced Q13 which was originally 2SC983 with a KSC2383 after reading a previous thread. Would anyone have any ideas as far as correcting this issue? I replaced coupling caps previously.

    Bill
     
    Last edited: Jan 21, 2018
  13. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,874
    Location:
    Bensenville,Illinois
    Well, that wasn't it...

    what about c21 (100uf 50v) ?
    is it new?

    Q13 IS the time on delay for the power amp.

    As long as the power supply voltages are close. Please Check them.
     
  14. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Yes, C21 was replaced.
    I’ll record Power Supply voltages and post them.

    Bill
     
  15. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Voltages from board AWR-006 C but this is the 1973 SM based on most of my information.
    1. 29
    2. 0
    3. 57.9
    4. 28.92
    5. 30.47
    6. 0
    7. 12,53
    8. 19.68 VAC
    9. 19.69 VAC
    10. 12.75
    11. 0
    12. 0
    I can dig into it further tomorrow but that is initial readings

    Bill
     
    Last edited: Jan 22, 2018
  16. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Just a few other bits of info It seems to do it with or without preamp jumpers installed. It even happens with headphones, or so it seems to me.
    This amp seems to follow the 1973 Service manual but not in every case. I have both manuals so hopefully I can track it down.
     
  17. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,874
    Location:
    Bensenville,Illinois
    pin 10 is fine, all the voltages read at the power supply board are fine.
    pins 1, 4, 8 & 9 are all AC voltage points, so I am going to ASSUME that pins 1 and 4 are AC voltage readings.
     
  18. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    Mark, I was just about to get up and saw this so checked pins 1 and 4 again. Those were dc readings but I measured AC this time.
    Pin 1 and 4 both read about 21.6 VAC?
     
  19. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,874
    Location:
    Bensenville,Illinois
    With 5600 ohms and 100 microfarads, there is only a 7 millisecond delay. And NO regulated voltages are involved...

    The b1 and b2 voltages come off of the raw DC big capacitor, (56 to 52 volts dc C3 3300uf 63v) which also (unusually) feeds most of the regulated voltages.

    The big cap is original?
     
  20. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    390
    Location:
    Pleasanton, TX
    The big cap was changed. I used a 6800 63V in its place based on other threads.
    I am reading 57.3 volts at the cap.
     

Share This Page