No sound sx 838

Discussion in 'Pioneer Audio' started by Pickup1963, Jun 8, 2018.

  1. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I have a jumper on protection relay and no sound I can hear the relay click that's all up for suggestions
     

     

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  2. markthefixer

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

    Messages:
    21,012
    Location:
    Bensenville,Illinois
    Do not jumper the protection relay!!!

    Relay clicking once after a several second delay means the amps have no faults, and the power supply is reasonably correct.

    Being a new member, I HAVE to ask: are the preamp out - power amp in jumpers in place in the back, do you have a service manual and understand how to set the switches for sound? This unit DOES have extra counter-intuitive switches.
     
  3. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    Yes the jumpers are in place and I do have a service manual. First the protection relay does not click when the unit is turned on.
     
  4. mbz

    mbz AK Subscriber Subscriber

    Messages:
    1,947
    Location:
    Melbourne, Victoria
    Remove the jumpers.

    Then maybe a fault in the protection circuit or the protection circuit is doing its job.
    The next step probably involves voltage measurements on a powered up unit. Are you comfortable with this? (lethal voltages inside)
    Also do you have the tools (multimeter...)
     
  5. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    Yes I'm comfortable with testing and I do have meter. I'm confused about when to use AC,DC or millivolt settings
     
  6. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,696
    Location:
    Glen Burnie Md.
    Most everything on the boards are DC Voltages. Look at the voltages coming off the Power Supply(AWR-055). You have AC coming in from the fuses, then it gets folded,spindled mutilated, and RECTIFIED into DC. All outbound voltages are DC, EXCEPT PIN 22 which feeds Pin 12 on the Protection board (AWM-025) and The Dial pointer lamp, Speaker Lamps, and the Tuning Dial Lamps. This is 7.5V AC.

    Does your meter Auto-Range or is it a manually selectable. If manually selectable, set it for 200VDC for most items. It should show you mV at that setting.

    Check the offset and bias voltages. Adjust them as per the manual. If they adjust ok, you should get sound. Push in SPKR "A", Make sure all Toggle switches are UP (Tape Monitor especially), and turn selector to AM or FM. See if you at least get AM static or FM static on each. If it will pick up a station, good.

    Cleaning the controls is the 1st step in any troubleshooting. Switches, and pots get dirty, and can disrupt the signal going thru them, even blocking signal. Cleaning them will allow the switches and pots to be ruled out in most cases. Get some DeOxit D5 or DNS-5 and Faderlube F-5. Read The idiots guide to DeOxit...Revisited.
     
    Last edited: Jun 9, 2018

     

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  7. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I will check those voltages and post my and post my result is
     
  8. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    Pin 1: -39.6. 2: -12.9 3: -.303 MV . 4: gnd. 5: -39. 6: -39 . 7: ,-275 MV. 8: ,-.309 MV. 9: 35.2 . ,10: 34.9. 11; 34.9 . 12: 7.3 ac no I don't know where to check bias and offset
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    ????

    Welcome to AK..
     
  10. mbz

    mbz AK Subscriber Subscriber

    Messages:
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    Location:
    Melbourne, Victoria
    are you working off the service manual?
     
  11. mbz

    mbz AK Subscriber Subscriber

    Messages:
    1,947
    Location:
    Melbourne, Victoria

     

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  12. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I was looking at that schematic, I don't have the 8ohm dummy resister is there some place i can order one by mail
     
  13. mbz

    mbz AK Subscriber Subscriber

    Messages:
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    Location:
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    Since the relay is not engaging the dummy load is not needed. More important to measure the dc offset ie, steps 2&3.
     
  14. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I tried steps 2 and 3 but I didn't get a millivolt reading I got a voltage reading of -41.5
     
  15. mbz

    mbz AK Subscriber Subscriber

    Messages:
    1,947
    Location:
    Melbourne, Victoria
    Yep, that would do it (fry the speakers), so the protection circuit has elected not to engage the relay. Next step is ti determine which channel is faulty
    then identfy the faulty parts.
     
  16. mbz

    mbz AK Subscriber Subscriber

    Messages:
    1,947
    Location:
    Melbourne, Victoria
    Which measurement pin (5 or 20) gave the -41.5V?
    Pin 5 indicates left channel fault, pin 20 points to right.

    If both pins had high voltage the faulty channel will be the one
    with the highest voltage, eg, -41.5 versus -41.3V.

    If the left channel is faulty, suggest diode test transistors
    Q7,9,11,13. Test Q8,10,12,14 for right channel, amp powered off/unplugged
     

     

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  17. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    OK I'll test them and get back with you
     
  18. mbz

    mbz AK Subscriber Subscriber

    Messages:
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    Location:
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    Diode testing of transistors can be a bit misleading, faulty components can sometimes pass. If they pass then
    measure Vdc to ground/chassis for base then emitter then collector of the listed transistors. Please don't probe
    between transistor legs, probe at connecting part eg a resistor, diode, cap...
     
  19. Pickup1963

    Pickup1963 New Member

    Messages:
    22
    I apologize if I seem a little ignorant....this is the first time I've tried anything like this. If this was a vehicle I could fix it no problem. Are all those you told me to test on the same board having a hard time locating. Your patience is appreciated
     
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  20. mbz

    mbz AK Subscriber Subscriber

    Messages:
    1,947
    Location:
    Melbourne, Victoria
    The transistors should on the board mounted to the large heatsink, so it
    won't be so easy to test. However pins are available for the output transistors
    Q11,12,13,14

    upload_2018-6-10_21-8-52.png
    will look at other transistors
     
    Last edited: Jun 10, 2018

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