sx-939 static

Discussion in 'Pioneer Audio' started by kcmoejoe, Oct 28, 2009.

  1. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Checked all grounds, everything looks tight and getting .01 - .02 ohms on chassis connections. When this started a few weeks ago it was in the right channel and intermittent, small bit of static then would go away for 5-10 minutes but keep coming back. Now, it's constant. The only other thing I noticed was the Aux selector switch light bulb is out. But, it went out awhile back before this issue cropped up.
     

     

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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    21,612
    Location:
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    The lamp shouldn't be related as it's on an AC circuit. It's either a Resistor, cap, or a transistor. Check underneath the boards you worked on and look for cold solder joints. Retouch them with new solder. Test.

    With nothing connected to the tape monitors or the Dolby NR switch, cycle them one at a time with the unit on. Leave on for 5-10 seconds and see if the static is there. If all are quiet then the problem is before the tape monitors, or The Dolby NR. Also cycle the MONO Switch. If they are all quiet whn engaged the problem is in the EQ Amp, Mic board, or switch gangs that are dirty.
     
  3. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Duplicate ON = static
    Tape 1 ON = no static
    Tape 2 ON = no static
    Dolby NR ON = no static

    Mono ON = static

    This is all done with the Aux input selected. The mic board is the same as the bd the Aux switch is mounted to, right?
     
    Last edited: Jun 9, 2018
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    IIRC the mic bd is right behind the Mic Jack's. The static problem is in the EQ or Mic board. Chopstick and Chiller time.
     
  5. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    The mic inputs on the front have wires that run over and connect to AWS-069 that is for the AM thru Aux function buttons.

    So, focusing on the EQ board, I've replace (again) all 8 transistors. Should I focus on the caps now having gone bad, then the resistors (these have to be checked with one leg lifted, correct) ?
     
  6. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Have you cleaned the switches on AWS-069? If not do so with DeOxit and follow up with Faderlube. There are times when more than 1 or 2 repeat applications are needed on these. The function switches on the 838/939/1010 have a bad tendency to go noisey. I would just check the caps to make sure polarity and install match, but start checking the resistors (yeah pull a leg on each). If any are out of spec by more than 5% replace. And check the AWS-069 for cold solder joints. Hold off on shotgunning it (eq board) until you've tested and checked.
     

     

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  7. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    I have really soaked all the function switches, keep thinking the AUX is faulty of course. Just went back and faderlubed them all. So help me understand, If the switch was oxidized would it only cause one channel to have static? I will take another look at AWS-069 for cold solder joints. I touched up a few that looked uneven. Then, on to checking resistors...this could take awhile.
     
  8. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Remember that the function switches have both the L & R channels running thru each one. So yeah you could have one channel that is oxidized more than the other which could casue drop offs and static as the preamp tried to push the current thru oxidized contact(s). It's possible that the switch is faulty and non recoverable.
     
  9. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Ok, good to know. thanks for the info. So far I've tested 8 resistors on EQ. See if I'm on to something here...all check within 5% except R26 (believe it's the R channel) suppose to be 1.5k ohm - reads .673 ohm. to compare I tested L channel R 25 1.5k and it reads 1.472 ohms.
     
  10. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Go ahead and replace both if you have on hand. R26 is bad provided you lifted one side. If you can match them close, all the better. These are part of the Mic output from the EQ board. This may probably be the culprit.
     
  11. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    R26 was the only bad reading on all the EQ resistors...will place order and replace as a pair for both channels. I went ahead and got 100 ohms for the AWS-069 board if I need to troubleshoot it next. Thanks so much for your help narrowing it down Larry.
     

     

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  12. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
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    well darn, that wasn't the problem. Upon further inspection of R26 it had a different color code (680 ohm) than R25 so it wasn't bad, just had the wrong value installed before I had the unit. I did get my hands on the correct 1.5k and installed it, so they now match very closely at around 1.470 ohm.
     
  13. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    21,612
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    I can't remember if the mic plugs short or not when no jack is installed. If they do Short, there may be corrosion on the parts causing a high resistance. THAT can cause problems.
     
  14. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    I used a 1/4" headphone plug and deoxit and worked it in and out of the mic inputs, didn't seem to affect it. The static noise just continues and sometimes gets a little louder and pops in and out. guess i should start testing resistors on the AWS-069 board next.?
     
  15. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    I asked a guy (Jordan Pier) on youtube who does professional service and this was his reply... Leakage of voltages in push button can cause this. No easy fix I'm afraid. Might be leakage through the board too. Definitely true for sets near the beach. Best bet is to harvest a complete board with switches from a donor.

    Is this what you meant about the Aux switch being non recoverable?
     
    Last edited: Jun 11, 2018
  16. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    21,612
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    Pretty much. The Switch board's are separate from the Control amp board. But the switches are sealed base to case so they can't be opened. However they can be sprayed with DeOxit thru a small triangular hole in one of the front corners. If DeOxit doesn't take care of it, it may need a new switch. Let me check something and I may have you jumper the on leads for AUX temporarily to see if noise abates.

    Jumper the following pins on the AWS-069 board Do it at the pins. Pins 3 & 45, Pins 4&5, Pins 8&9 This will put the AUX in the ON Position (while the actual switch is in off). If the static continues, then the 100ohm resistors are probably at fault as they are in circuit, as they are between pins 4 & the switches for one side, and pin 9 & the switch on the other. To rule out or Rule in the resistors lift one side of both resistors and jumper to the switch side of the resistor instead of the pins.
     

     

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  17. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
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    Ok, did the jumpers on the pins and made sure the aux switch was out (off) nothing selected. It started off quiet, turned volume up a bit then the static started coming back.

    Not sure I'm following you about ruling out or in the resistors. Can I just test them one at a time with one leg lifted for 100ohm value? R10 was 98.8 and R11 was 101.5

    could it be any of the resistors on the board at fault, or just the two connected to pins 4 and 9?

    to rule them out, you're saying to leave all the pins jumpered and then jumper one resistor at a time to both it's legs but with one lifted?
     
    Last edited: Jun 12, 2018
  18. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Lift R10 and R11 on the pin side of the resistor. Then take a jumper wire with a 100ohm resistor attached in series with the jumper and go from the pin to the unlifted side of R10 or R11. Turn on the unit. See if the static comes in. If it does R10 and R11 are not at fault.
     
  19. kcmoejoe

    kcmoejoe Active Member

    Messages:
    106
    Location:
    Kansas City, MO
    Ran the test on R10, R11 just like you said and still have the static...so that rules out the two in series with the aux switch, they did test within 5% of 100ohm.

    I noticed while no buttons are selected it still has static also, is that because the two resistors are lifted from circuit?
     
    Last edited: Jun 16, 2018
  20. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,612
    Location:
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    I doubt it. This is a definate headache. Remove the Jumpers btwn the amp and preamp. Then turn it on. if the static is there it's in the AMP. Then connect the preamp to another amp to double check the preamp. report back with results.
     

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