1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

SX 1050 power supply problems

Discussion in 'Pioneer Audio' started by JTF, Aug 9, 2018.

  1. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    I recently picked up a SX 1050 that would power on but had no sound output. I am not getting the second relay to click. I opened it up and found the F1 and F2 fuses on 104 board were blown, replaced them and still would not work. Fuses are not blowing now but checked the voltages on the 103 board and found most were off. I replaced all the caps and most of the transistors on that board but still have issues with voltages at pins 13,15 and 16. Some of the others are off just a little. I suspect Q1 may be problem. Q1, Q9 and Q12 are only ones I did not replace. I did find a couple of the transistors were bad when I was replacing them. Was planning to go back in and replace the rest of these but thought it might be good idea to ask the guys here that have good working knowledge of these if there is something else I should be looking at.
     

     

    Please register to disable this ad.

  2. Watthour

    Watthour Electron Rancher - JS3600

    Welcome Aboard!

    What are the voltages at the various PS output pins?
     
  3. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    Pins on AWR-103 power supply board:

    Pin 5 = 13v
    Pin 7 = -13.6
    Pin 8 = -62.6
    Pin 9 = -31.8
    Pin 10 = -28.2
    Pin 13 = -7.6
    Pin 15 = -1.6
    Pin 16 = -1.1
    Pin 19 = 5.1

    Main filter caps are +/-61v
     
  4. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    432
    Location:
    High Plains, Eastern Colorado
    Welcome to AK :)

    Q1 is a suspect, as well as Q2 and Q9, or R1.
    Test or replace those 3 transistors.

    What is the voltage on AWR-103 at:

    Pin 2* =
    Pin 3=
    Collector of Q1=
    Positive side of C1=
    Cathode of D1=

    *If Pin 2 is not close to +76 vdc, check at AWR-104 pin 6. If pin 6 is not +76 vdc then (with power off) test D2, D3, D4 & D5 on AWR-104.

    With power off measure R1, it should be 10 ohms. You may need to lift one end.

    EDIT: more info
     
    Last edited: Aug 10, 2018
  5. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    OK, first thing I tested was R1 and it is bad. Need to get 10 ohm resistor then I'll check more. I did check all the diodes on AWR 104 previously and they were all good.

    Should I stay with 1W for R1? Metal film?

    Should I replace the other resistors on the 103 board that look kind of heat discolored. They are not badly discolored just slightly.
     
  6. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,816
    Location:
    Las Vegas Nevada
    Bad?
    What was the reading?
     

     

    Please register to disable this ad.

  7. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    I found a 10 ohm 2W metal oxide in my parts, OK to use?

    Reading was jumping around in the m ohms
     
  8. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    432
    Location:
    High Plains, Eastern Colorado
    For R1: It is listed in the Service Manual as 'Metal Oxide' which has better thermal ratings than Metal Film ( http://www.resistorguide.com/metal-oxide-film-resistor/ ). I would stick with Metal Oxide or wirewound. Do not go below 1 watt rating, higher is OK. If you cannot find a metal oxide or wirewound go with a higher wattage rated metal film (>/= 2 watts.)

    Discolored resistors should be measured, replace if out of spec.

    Did you test Q1, Q2, Q9?
     
  9. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    Took the sock off and it blew the outer layer off. IMG_1524.JPG
     
  10. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,816
    Location:
    Las Vegas Nevada
    I think you should stay with a one watt replacement(?) The 10 ohms is more of a fuse than anything. Raise it up from the board.
    The circuit should be fine but the DBT will tell the story.
    Note: Look at R19 its sister. Its a 2 watt? It is providing an additional -13v supply that R1 is not.
     
    Last edited: Aug 10, 2018
    merlynski likes this.
  11. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    I replaced Q2 already and tested Q1 and Q9 out of circuit when I replaced all the other transistors. When I get R1 back in I will test voltages again.
     
    merlynski likes this.

     

    Please register to disable this ad.

  12. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    432
    Location:
    High Plains, Eastern Colorado
    Looks a bit toasty :).

    Point well made! I was thinking of it primarily as 'ballast' to reduce the power dissipation of Q1. I learn new things every time I visit AK :thumbsup:.
     
    Last edited: Aug 10, 2018
  13. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    Yes, R19 is bad also. Burned spot on it and measures 111 ohm
     
    merlynski likes this.
  14. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    All the rest of the resistors with socks test OK
     
    merlynski likes this.
  15. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    Replaced R1 and R19. Powered on and checked voltages on AWR-103 pins.

    Pin 1 = 18.7
    2 = 63.5
    3 = -64.1
    4 = 0
    5 = 13
    6 = 13
    7 = -13.6
    8 = -62.1
    9 = -31.5
    10 = -25.6
    11 = -25.6
    12 = ground
    13 = 24.9
    14 = 24.9
    15 = 30.9
    16 = 61.3
    17 = 61.3
    18 = 5.2
    19 = 5.2

    The DBT is slightly glowing so think there are more issues to deal with. I still do not hear 2 clicks of relays. Only hear the relay by surge resistor, clicks on after 1 second.

    Measurements of transistors:

    Q1 B= 62.1
    C= 62.8
    E= 61.5

    Q2 B= 62.6
    C= 62.8
    E= 62.1

    Q9 B= 13.7
    C= 17.5
    E= 13
     
  16. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    Further checking on AWR-104 board, I'm seeing different voltages than previous check.

    Pin 3 = 48.5v
    5 = -48.5
    6 = 63
    7 = -63.7
    8 = 18.6

    The Main filter caps are now reading +/- 48.5v
     

     

    Please register to disable this ad.

  17. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    432
    Location:
    High Plains, Eastern Colorado
    Voltages should be on the low side while on the DBT, and DBT glowing orange is probably OK. What wattage is the DBT bulb?
    I would expect the voltage on AWR-103 pins 8, 9 and 10 to be lower (less negative) than their nominal voltages rather than higher as you list. Did you test/replace Q5, 6, 7, and 8?

    Sounds like the soft-start circuit is working ok, a bit slow because of the DBT.

    The protection circuit relay may not pull in while on DBT.

    Make a quick DC offset voltage check of the power amp outputs, AWH-047 pins 4 and 17. Are they less than +/- 50 millivolts?
     
    Last edited: Aug 10, 2018
  18. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    I have a 150w lamp in the DBT. I replaced Q5,6,7 and 8. Measurement check on AWH-047 Pin 4= 2mv and Pin 17= 3.5mv. I have not touched the bias - offset pots yet.

    Q5
    B= -62.7v
    C= -63.8
    E= -62.1

    Q6
    B= -63.4
    C= -63.8
    E= -62.9

    Q7
    B= -14.1
    C= -63.5
    E= -13.7

    Q8
    B= -32.2
    C= -45.2
    E= -31.6

    Thanks for all the help and quick responses from you guys, a wealth of knowledge here. Just wish I understood circuits and reading schematics better.
     
  19. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,816
    Location:
    Las Vegas Nevada
    The PS voltages good good. You could use the 100 watt but the 150 is okay.
    On the DBT check set the amps. DC Balance and idles.
    Read the settings but hold off on the adjustments until you get back to us with the readings(?)
     
    merlynski likes this.
  20. JTF

    JTF AK Subscriber Subscriber

    Messages:
    21
    DC offset on pin 4= 1mV, pin 17= 3mV

    Bias across pins 2-6= 37.1mV, pins 15/19= 37.5mV

    Measurements taken after only on for about 5 min.
     

Share This Page