Pioneer Spec 4 loud arcing sound through speaker - Help

Discussion in 'Pioneer Audio' started by daveyh, Feb 14, 2018.

  1. daveyh

    daveyh AK Subscriber Subscriber

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    I have a Pioneer Spec 4 amplifier that I need some help diagnosing. It has been recently recapped including the big filter caps and boards. I am looking at it for a friend of mine and I did not do the work on it.

    The problem is it sounds great for about 10 minutes and then out of the blue a LOUD ARCING noise or extremely loud POP will come though to the speakers and scare the crap out you. Loud enough for me to turn it off without hesitation. It happens with no warning. I checked the DC offset and it is fine when I first turn it on. The relay clicks in nicely. It sounds great, for awhile. Is this DC current hitting the speakers after is in on for awhile? What would cause this? Anyone have this problem before or know where I should look first without throwing leaves to the wind?
     

     

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  2. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Is it from both speakers?
    If so, a Power Supply issue.
    If one side, then an amp assembly.
    Regardless. Check the other guys work.
    Sounds crazy but recheck the big caps for proper install/connections - paying close attention to the connections.
    What brand of components were used in the recap?
    Taking on this amp is going to be more work than a standard repair.
    You almost have to start from the beginning.
    The issue will probably be visual.
     
    Last edited: Feb 14, 2018
  3. daveyh

    daveyh AK Subscriber Subscriber

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    I took off the top and bottom and rechecked the DC offset and bias, Both are good. The left channel however is not a constant right on when I connect my meter to the speakers terminal. It fluctuates but never goes over 3.2mA and then goes back down and then up and so on. I did notice that only one relay, the one on the left side clicks off and then back on and I think this is the channel with the problem. I am thinking that is causing the arching or load pop when it clicks off. It may take 10 minutes or it could take 3 minutes while being on. I do not have it connected to speakers at the present time.

    I did notice on both boards the C1 and C3 capacitors have both been replaced with 100v 120uf instead of the 100v 80uf capacitors listed in the service manual. They look like they were pulled from another unit since the have glue on the side of them but not on the circuit board itself. Also it looks like the outputs transistors were changed to MJ21193G and MJ21194G but the old thermal grease or insulators were left intact. The big filter caps are big and are made by Nippon CC.

    Going to pull the amp assembly as suggested and check it again. Going to be a long day.

    Thanks for your response!
     
  4. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    The replacement caps are fine rating wise but I wonder if you should replace the cap set with new forum listed components? There's not that many in the amp. This will give another worthy reason to look over the entire unit.
    There's not that much to it.
    The On-Semi outputs are a good choice.
    Your saying the popping is on one channel?
     
  5. daveyh

    daveyh AK Subscriber Subscriber

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    New forum listed components? Where is that at?

    The loud arcing sound through the speaker I think is only coming from the left relay when it goes into protection.
     
  6. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Last edited: Feb 14, 2018

     

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  7. daveyh

    daveyh AK Subscriber Subscriber

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    Well it is clicking on and off on one of the relays on the power amp board on the left side looking towards the front of the amp. Now after replacing some components according to the parts list is now more frequent. It now clicks on and off about every two minutes or so. I pulled all the outputs on that side, checked them and put in new thermal grease and Mylar insulators. Checked the board for bad solder joints under a large magnifying glass and lamp. Done for tonight. I will make a list of what I replaced tomorrow. Really don't know why it's doing what it is.
     
  8. daveyh

    daveyh AK Subscriber Subscriber

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  9. daveyh

    daveyh AK Subscriber Subscriber

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    Where is the protection circuit located? The amp section or the meter board. Mine is the A amplifier board.
     
  10. petehall347

    petehall347 the brandy coffee man Subscriber

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    looks like a flaky transistor issue to me
     
  11. daveyh

    daveyh AK Subscriber Subscriber

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    That's what I thought at first I have been pulling each one and checking them but they all check to be good. So far have not found the culprit.
     

     

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  12. petehall347

    petehall347 the brandy coffee man Subscriber

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    might well look good on a meter . freeze spray and heat should find it . or at least get close.
    i always find heat from my iron might fix them for x amount of time . so removing and testing even fully powered might not reveal anything . once had a tv i could fix and it would last for weeks just by warming up a transistor on the rear of the gun on the tube , think it was to do with green . long time ago but flaky transistors can be rather sporadic . check numbers against the lists of known bad ones . most likely close to differential .
     
    Last edited: Feb 14, 2018
  13. petehall347

    petehall347 the brandy coffee man Subscriber

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    use old crappy speakers till its fixed .
     
  14. UncleBingo

    UncleBingo AK Subscriber Subscriber

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  15. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    The 2SC1384, Q13 is the hold in for the relay. The 512-KSC2690AYS is a better more robust replacement.
    Q8 thru Q13, Protection circuit transistors are on the meter board.
    Rebuild it with new caps and transistors. As long as the amps are stable.

    From MattsSD restoration thread:
    Meter Amp Board (AWM-113) (Q8 and 9 should be gain matched) (Check board revision number, the A version has C1 as a 100uF 25v CEA cap and C11 as a 100uF 80v CEA cap)

    AWM-113: C1: 220uF 10v CEA: 647-UPW1A221MED 220uF 10v
    AWM-113: C2: 2.2uF 50v CEANL: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWM-113: C3: 470uF 6.3v CEA: 647-UPW1A471MPD 470uF 10v
    AWM-113: C4: 470uF 6.3v CEA: 647-UPW1A471MPD 470uF 10v
    AWM-113: C7: 3.3uF 63v CEA: 647-UPW2A3R3MDD 3.3uF 100v
    AWM-113: C8: 3.3uF 63v CEA: 647-UPW2A3R3MDD 3.3uF 100v
    AWM-113: C11: 47uF 80v CEA: 647-UPW2A470MPD6 47uF 100v
    AWM-113: C12: 47uF 80v CEA: 647-UPW2A470MPD6 47uF 100v
    AWM-113: C13: 330uF 100v CEA: 647-UPW2A331MHD 330uF 100v
    AWM-113: C14: 330uF 100v CEA: 647-UPW2A331MHD 330uF 100v
    AWM-113: C16: 33uF 25v CEA: 647-UPW1V330MDD 33uF 35v
    AWM-113: C17: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
    AWM-113: C18: 470uF 6.3v CEA: 647-UPW1A471MPD 470uF 10v
    AWM-113: C19: 470uF 6.3v CEA: 647-UPW1A471MPD 470uF 10v
    AWM-113: C24: 2.2uF 50v CEA: 647-UPW1H2R2MDD 2.2uF 50v
    AWM-113: C25: 2.2uF 50v CEA: 647-UPW1H2R2MDD 2.2uF 50v
    AWM-113: C26: 2.2uF 50v CEA: 647-UPW1H2R2MDD 2.2uF 50v
    AWM-113: C27: 2.2uF 50v CEA: 647-UPW1H2R2MDD 2.2uF 50v
    AWM-113: C28: 3.3uF 50v CEA: 647-UPW1H3R3MDD 3.3uF 50v
    AWM-113: C29: 3.3uF 50v CEA: 647-UPW1H3R3MDD 3.3uF 50v
    AWM-113: C30: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
    AWM-113: C31: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
    AWM-113: C32: 47uF 25v CEA: 647-UPW1V470MED 47uF 35v
    AWM-113: C33: 47uF 25v CEA: 647-UPW1V470MED 47uF 35v

    Q8: 2SC945: 512-KSC945CYTA
    Q9: 2SC945: 512-KSC945CYTA
    Q11: 2SC945: 512-KSC2383YTA
    Q12: 2SC945: 512-KSC2383YTA
    Q13: 2SC1384: 512-KSC2690AYS
     
    Last edited: Feb 14, 2018
  16. mattsd

    mattsd AK Subscriber Subscriber

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    Use the 512-KSC2383YTA in place of the KSD1616.
     

     

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  17. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Edit completed;
    Thanks Matt.
     
  18. daveyh

    daveyh AK Subscriber Subscriber

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    I think it's FIXED! Thank for all who helped me! :)

    Rebuilt the amp board with new transistors per post. Only did the bad side. The meter board had already been rebuilt. I would install a few transistors at time, install the heat sink back on and check for problems. It turned ou to be the last set of transistors I installed. Wouldn't you know it. Q4 and Q5. Replaced them with KSC3505 / KSA1381ES. Been playing it for awhile and no arcing sound through the speaker. Sounds very nice. Running it trough my Dynaco Tube pre-amp recently recapped. So far so good.

    After installing Q4 and Q5 I got a very stable reading when checking the bias and offset. That I was not getting before. It would fluctuate.

    Both right and left channels are set at 50mA bias and offset at 0v but the amp board I fixed is running 5 to 7 degrees warmer than the other channel. Do you guys think that is a problem? The heat sink is warm to the touch and the other side is cooler. I also used a laser heat gun and they are 95 and 102.
     
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  19. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Good. I guess the small fluctuations were bigger than the meter could show?
    Another method would be to monitor the amps output and catch it when it trips the protection.
    Nice save.
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

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    well done :thumbsup:
     

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