Pioneer SX 828 recapped - Relay click on and off

Discussion in 'Pioneer Audio' started by havols, Apr 23, 2017.

  1. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Hi Audiokarma Members
    I wrote from Manaus, Brazil.
    I have here a Pioneer sx 828, in great condition.
    Here in Manaus, Brazil, is hard to find some technician to do a good service on this vintages amps.
    So, I've learned a lot with a help of audiokarma friends, and myself have did maintenance of my integrated and tube receiver and amplifier.

    In this sx 828:
    Except the 2 main caps, I replace all others eletrolitic caps, and a little transistors by AF-UNIT and HEAD-AMP-UNIT.
    In the main amp Unit, i just replace the eletrolitics caps.
    I regulated the bias Voltage
    BIAS 11-17 PIN: 18mV
    BIAS 12-18 PIN: 21 mV
    When i power on the receiver, it sounds fine for about 4 minutes, the Bias voltage increase to 29mV, and stabilizes in this value.., and after some minutes, the relay click ON (no sound), and after a time, the sound return.... and the relay click on again, no sound... and sound return...

    2 Main Caps are original. Follow the voltages on power supply

    PIN = Voltage on SCHEME = Voltage by this sx828
    2 = 12V = 12.2V
    4 = 4.5V = 4.3V
    5 = 32V = 30.9V
    6 = 31V = 32.4V
    7 = 35V = 34.6V
    14 = 44V = 45.5V
    15 = -44V = -45.4V
    17 = -45V = -46.1V
    The voltage on Wall is 117V (120V on receiver)

    If anyone can help me, i will appreciate.
    Best regards
     
  2. markthefixer

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

    Messages:
    20,730
    Location:
    Bensenville,Illinois
    in response to a PM:
    [​IMG]
    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber
    Messages:
    20,287
    Location:
    Bensenville,Illinois
    I do not do "private" help, all questions are handled in the Forum, where everyone else can benefit when the problems are fixed - otherwise there would be nothing to read!! It does seem that you have done a LOT of reading, and are quite advanced into the process. Even more impressive when the fact that there is no sx-828 reference restoration thread with parts lists.

    Please start your very own thread in the Pioneer Audio forum. EVERYONE deserves their own thread.

    In it we will have to figure out which of the many possible causes it is.
    It could be as simple as the awm-025 q7 relay driver transistor being weak ( heating and cooling cycling)
    replacement: 512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40
    (is it still original? if not did you add a 1n4004 diode at pins 9 and 10(cathode - banded end) across the relay coil?)

    Or the protect circuit may be doing it's job correctly, and something else is at fault:

    The main amp can have 2sa726 transistors (that is a nasty surprise) that should be replaced with ksa992 transistors.
    quite frankly the whole main amp could benefit from new silicon AND trimpots (vr3,vr4 especially)

    this is from my old notes,I have never had enough time to write this up:
    sx-828 main amp,
    input differentials:
    2sa572 to-92 bce 50v 0.05a 0.2w 160-960hfe 80MHz Ft
    use:
    512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

    vas and bias stage:
    2sc1124 140v 1a .95w 160hfe 120MHz Ft
    use:
    512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40


    drivers:
    2sa484 to-5 ebc 110v 1.5a 0.8w 30-300hfe 20mhz
    2sc484 to-5 ebc 110v 1.5a 0.8w 30-300hfe 20mhz
    use:
    512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
    512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54


    outputs:
    2sa680 pnp to-3 120v 12a 100w 40-140hfe 6mhz
    2sc1080 npn to-3 120v 12a 100w 40-140hfe 6mhz
    use:
    534-4662 to-3 mica insulators $0.16 each
    863-MJ21193G pnp to-3 250v 16A 250W 4mhz 8-75hfe $3.83
    863-MJ21194G npn to-3 250v 16A 250W 4mhz 8-75hfe $3.83

    These main amplifier transistors HAVE been done in some sx-828's and IF there were problems, I would have expected to hear about them at least 4 to 6 years ago.

    Other people have been where you are at, do not reject their counsel in the forum, as I am not on the forum very much while I am on "hiatus".
    I try to watch for problems, and provide steering towards solutions when I do get time to go on the forum.

    mark
     
    havols likes this.
  3. markthefixer

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

    Messages:
    20,730
    Location:
    Bensenville,Illinois
    By PM:
    BC and BD series will do

    the single 1n4004 diode can be any general purpose rectifier with 200v rating or greater.
    it is connected across the relay coil,
    when the relay is turned off, the magnetic field collapses,
    and this makes a voltage "spike" that slowly damages the relay driver transistor.
    The diode is arranged so that the spike is limited to 0.6 volts. it is done like this in many later and higher powered Pioneer models.
    If the diode is backwards the relay will not operate and the power supply will probably be damaged, because it forms
    a better path than the relay coil, and with minimal resistance - looks like a short circuit.

    the anode or non banded end is connected to pin 9, the cathode with the painted on band (+) connects to pin 10
    that is true for both the w28-008 and the awm-025 protection board(s).
     
  4. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    20,436
    Location:
    Glen Burnie Md.
    havols; I was going to suggest upgrades and mod to the protection board (awm-025 ) but I see Mark beat me to it. Do all of his recommended replacements, and recheck the unit (power on and working?) after each 3 parts. The diode mod in these early units is literally worth it's weight in gold (Inca or otherwise!) as Pioneer did this in later units.
    In addition to the 2sa726, the 2sa725 is another protagonist. replace it with the KSA992 or the equivalent Bx transistor.
    Update us with progress here in the forum and we'll try to help you get up and running correctly.

    Larry
     
  5. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Thanks Larry and Mark
    I'm happy with your help.
    I'll make changes. In a few days post the result.
    Regards.
     
  6. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Hi guys
    I install a diode 1N 4004 in the protection board AWM-025. Non banded end on PIN 9, and banded end on PIN 10..
    The receiver plays fine, but after 5 minutes, the relay click on... and stills mute... until now.
    I wait for 8 hours, and power on again, and no relay click.. no sound

    I measure the voltages on AWM-025 Board.
    PIN 2: -12.6 V
    PIN 11: +34 V
    PIN 10: +33.7 V
    PIN 9: +33.7 V (Problem???)

    The three diodes D5, D6, D7
    Cathodes end by 3 diodes: around 20V. Ok with schematic

    Anode D5, D6, D7: 1.44V
    Base Q5: 1.44V
    Base Q6: 0.72V

    Here can be the problem too?
    Maybe R22, R23, R18?

    Best regards Guys
     
  7. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    PIN 12: 6.8 VAC
    D8 appears OK
    R22 and R18 is perfect.
    Regards
     
  8. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Hi Larry and Mark
    I replaced Q7 AWM-025 board by 2SC2690 A-Y.
    I Add a 1N4004 diode across pin 9-10 in AWM-025 board
    I replaced 2sc1124 in main amp board by new ones 2SC2690 A-Y
    I checked VR3 and VR4 and it is fine.
    I don't replace the 4 transistors 2sa726 in main amp board.

    So, at now, the situation is: Power on, and can't listen the relay click, and no sound on outputs. I will replace the 4 2sa726 transistors in the next days.

    I am waiting for 3 years to listen this sx 828...
    for a long time it has this problem .. and i like so much this receiver
    Thank you very much for your help.
    Regard
     
  9. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    I measure now, and found the same voltage on PIN 9 and 10 by AWM-025 board.
    PIN 9: 34.2 VDC
    PIN 10: 34.2 VDC
    It is a problem right?
     
  10. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    20,436
    Location:
    Glen Burnie Md.
    Yeah. When the Relay is energized Pin 9 should be around 9V. The transistor (Q7) is NOT being turned on. check voltages on all legs of Q7. Also check the Base of Q6 and the Base-Emitter of Q5. Check C6 and C5 or replace if not done already.
     
    havols likes this.
  11. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Yeah Larry
    I replace Q7 by another new one.
    Great. The relay clic, and had sound on output.
    After 5 minutes, relay clic again, and non sound
    So, i adjusted Off sett and Bias
    Offset L: 002mV
    Offset R: 003mV

    Bias L: 15mV
    Bias R: 19mV

    But the relay stills clic on.

    When i measure the PIN 9 of protection board. there's a 34V again.
    I think that the problem is not the transistor.
    Regard
     
  12. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    I refixed some welds, and it sounds great again
    For about 10 minutes, and gave a quick click of 2 seconds (cut the sound). Then the sound came back again for about 10 minutes, and another click (sound cut) for 2 seconds, and sound great again.
    What I noticed was that the Bias voltage increased slightly (to about 29mV) after about 20 minutes power on.
    The 4 VR on output board stills original yet. And the 4 2sa726 transistors too.
    I will find the pieces to replace then in next days. After i will post results here.
    Maybe the variable resistors can be unstable larry? Can be the cause of relay clic?

    Regard
     
  13. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Larry. Volteges on AWM025, when relay is active (no sound)
    Q7
    B: 8 mV
    C: 34 V
    E: 0 V

    Q6
    B: 0.69 mV

    Q5
    B: 9.6 V
    E: 10.3V

    C6 and C5 are good (new)
    Thanks to your help
    Regards
     
  14. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    More informations:
    In AWM 025:
    The cathode side from D5 had just 11V. The cathode side of D7 and D6 had 19V.
     
  15. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    20,436
    Location:
    Glen Burnie Md.
    Look at the power supply voltages at pins 7, 19, and 21, both during NORMAL Operation and again when it acts up. Make a list of the voltages for both conditions. I'm leaning towards a POWER SUPPLY problem. I'd check all P.S. voltages during NORMAL OPERATION and DURING PROBLEM OPERATION.
     
  16. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Larry
    Now, the receiver is only with relay act up

    Pin 7: 34.6 Volts
    Pin19: 0 V
    Pin 21: 0V

    When act up, others voltages on power supply is:
    Pin:
    2: 12.2 V
    4: 4.3 V
    5: 30.9 V
    6: 32.4 V
    7: 34.6 V
    14: 45.5 V
    15: -45.5 V
    17: -46.1 V
     
  17. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Hi Larry
    The relay stills blocked
    Can you help me a bit more... to fix this SX 828.

    The power amp board is OK. Offset and bias is fine.

    In power supply, I replaced:
    R12: install 330 ohm 3W
    Q3 2SD313: Install MJE15032E
    Q1 2SD234: Install SC2073.
    Now, the voltages on power supply Pins are fine. Just like the schematic.

    In protection Board, i replaced;
    Intall 1n4004 diode in pin 9-10
    Q7: install a SC2690A.
    Q6: Install a BD 546.
    The voltages on this board is OK, except in Pin 9, that is 34V. When the relay is OK, the voltage on PIN 9 is 8V. When blocked, the voltage is 34V. Now it stills blocked.

    I think, that the problem is in protection board.
    Follow the voltages on transistors by protection board (AWM025)
    Q5:
    B: 10.8V
    C: 0.69V
    E: 11.6V

    Q6:
    B: 0.68V
    C: 8mV
    E: 0V

    Q7:
    B: 8mV
    C: 34.2 V
    E: 0V

    Thank for your help
     
  18. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    20,436
    Location:
    Glen Burnie Md.
    Havols; Right now I'm going thru burying my wife who died on the 17th. It might be a while before I can do anything but so far it looks like the transistor voltages are pretty much ok. I would suggest you pull the relay for now and clean the contacts (both NO and NC sides) with DeOxit on a piece of paper. pull paper only one way and one time with each piece of paper. replace all the caps on the board too and test after everything.

    Larry
     
    havols likes this.
  19. rcs16

    rcs16 Super Member

    Messages:
    2,972
    Location:
    Baldwin, Ontario, Canada
    Real sorry to hear Larry, my condolences, hang in there, be strong, my prayers go out to all.

    Rick
     
  20. havols

    havols Active Member

    Messages:
    133
    Location:
    Manaus, Brazil
    Larry
    My sincere feelings for your loss.
    God bless your wife, and give you the strength you need right now.
    Thanks a lot for the help.

    Regards
    Gustavo Naressi de Azeredo (Havols)
     

Share This Page