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SX-980 Protection Overload Condition

Discussion in 'Pioneer Audio' started by danyost, Dec 23, 2014.

  1. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    I have a Pioneer SX-980 Receiver that I purchased new in 1978. Some years ago, it started this never ending cycle of double-clicks (on and right back off) to the speaker outputs. The main unit stays on; only the speakers (both channels) are affected. Can someone point me in the right direction?
     

     

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  2. tsd71

    tsd71 RIP Tom Petty

    Messages:
    2,570
    Location:
    New Jersey
    Sounds like your DC offset is wacky, it could be a number of things but this is the easiest to check initally. If you have a multimeter and an insulated flat head screwdriver the adjustment is easy. Picture of the procedure is attached. Be concerned about the center voltage adjustment first. You will have questions and there are lots of people here who will guide you through this. Good Luck!:thmbsp:
     

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    Last edited: Dec 23, 2014
  3. markthefixer

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

    Messages:
    21,118
    Location:
    Bensenville,Illinois
    A question, is there a several second time delay before the first click after turning it on, and what is the time delay between clicks in the sequence of clicks?

    The amplifier board have two connectors on each going to the output transistors. The board side pins of these connectors turn black. Bad connections can be causing this.

    With the power off, long off, to allow the big capacitors to discharge, remove the plugs from the pins, and use a #2 pencil eraser, with a hole poked up it's center axis, push it onto each pin and twirl it to polish the pin bright.
    Then add a bit of deoxit to each plug's internal metal connections, and install and remove them a few times.
    After a few minutes of drying, try turning it on and see if the problem still shows up.

    BE VERY VERY CAREFUL, there is a pair of wires coming off the board, going to a component screwed onto the heat sink by the output transistors. They are the very fragile thermal bias diode wires, and they LOVE to break off flush with the body of the diode. DO NOT bend these wires any closer than 1/2" to the diode. They don't make them anymore. I can fix (it's a pita) them, but it's better to not break them.

    IF it continues, then pull out the preamp-out/ power amp-in jumpers and see if it stops.

    Next, try turning OFF the speaker switches to remove any loads. See if it stops.

    This type of Protect action is rather unusual.


    Further troubleshooting will require a service manual (download or buy - we can tell you where) and a DMM.
     
    Last edited: Dec 23, 2014
  4. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    Thank you tsd71 and mark the fixer for responding.
    I decided to re-establish the previous condition that I reported. (power on, about 5-7 seconds then start of repeating "click on and immediate click off"... evidenced by short bursts of sound)
    When I first turned on the receiver, I was able to listen to the radio for about 5 minutes. Then a click and no sound for about 1 minute. Followed by a click and sound for about 2 minutes, followed by a click and no sound for about 2 minutes... lastly, a click and sound for 30 seconds followed by a click and no sound for 5 minutes. I turned the receiver off.
    I let it sit for 10 minutes, turned it back on and no click/sound.

    Although this pattern is a bit different from my initial report, I do believe it still indicates the same issue.

    I did not check the DC offset, I did do all checks by markthefixer. I did note that the thermal bias diode wires are bent right at the diode attached to the heat sink but this was factory issue. I inspected them without wiggling and they appear to be intact.

    Shall I proceed with the offset check? BTW, the receiver has been powered down now for 15 minutes. I just turned it on, waited 30 seconds but never heard a click/sound. I turned it off.
     
  5. markthefixer

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

    Messages:
    21,118
    Location:
    Bensenville,Illinois
    Yes, you should first do the offset tests at the speaker terminals, no sound, just turn the volume all the way down.


    It sounds to me like the next thing to check is the base drive signal for the relay driver transistor. The transistor is being told to keep powered on continuously but is falling down on the job.

    BUT the important part of the answer is still missing:

    so I must explain:

    The click and no sound:
    when it clicks and there is NO sound
    if the sound is MISSING for the five to seven second delay
    or if it comes back FASTER.

    Five to Seven seconds means the protect integrated circuit is UNHAPPY with an input and is TELLING the relay to disengage ON PURPOSE
    This for example could be excessive DC offset...

    a faster return of sound indicates the relay driver transistor (q2, 2sc1438) is falling down on the job. DC offset could be ok.

    The base lead of Q2 on the awm-124 protection board can be tricky to get to, with danger of shorting other things nearby. The awm-124 protection board is tucked into the bottom of the chassis.

    It's best you download the same (32meg) service manual I am using so we are literally on the same page.

    Page 20 shows where the awm-124 protection board is

    Page 58 shows the board layout FROM THE BOTTOM!!! You will be looking at it from the top, a mirror image...

    See the words "foil side" at the top of the drawing?
    Q2 is right next to that. It has THREE connections. Two are parallel with the edge of the board, and a third is further in towards the center of the board.
    This third connection/lead is the one to measure.

    BUT it is done with the POWER ON (careful!!) and the music playing.

    The black DMM wire/probe goes to the bare metal chassis somewhere (ground)

    The red DMM wire/probe is what you measure around with.
    INSULATE ALL BUT THE TINIEST PORTION OF THE TIP OF THE PROBE WITH TAPE, so that when the probe slips (We ALL slip!! when we move our eyes to read the meter) no harm is done.

    The reading should be in the range of 0.7 volts (0.6 TO 0.8) when the relay is supposed to be on, and about 0.000 volts (well less than 0.1 volts) when the relay is supposed to be off.

    If the 0.7v stays when the relay clicks out, we have our culprit, q2

    If the 0.7v goes away when the relay clicks out, then the problem lies further up the line...

    To access the underside - stand the chassis on it's side with the bottom off, and it's best if the heavy power transformer is closer to the table top.
     
    Last edited: Dec 24, 2014
  6. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    I understand what you have instructed me to do. However, I can no longer get the receiver to a state where it "clicks" on. When I turn on the power, regardless the wait time (up to 15 minutes anyway) there is no longer a click. This tends to make me think that attempting the dc offset test would be a moot point. Is this correct?
     

     

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  7. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    So I guess the next question is "Can I test q2 under these conditions?"
     
  8. markthefixer

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

    Messages:
    21,118
    Location:
    Bensenville,Illinois
    SX-980 awm-124 protection troubleshooting

    Well, yes. Actually that is good news, a transient fault has become steady state. No hide and go seek, it's right there out in the open now.

    Read Q2 base, and if the protect system is TRYING to pull in the relay, and Q2 has fallen down on the job, we will KNOW. The presence of the D3 flyback diode across the relay coil has increased Q2's longevity in this model's design...

    If the q2 base voltage is far less than 0.6v, it's something else... and the protect chip isn't happy with something - which is why we check DC offset and the over current inputs, as well as certain power supply voltages and one ps voltage that signals a turned on condition.


    first read the base of q2.
    then these, posting the numbers:
    1. awm-124 pin 5 0.000v dc offset left
    2. awm-124 pin 8 0.000v dc offset right
    3. awm-124 pin 4 over 3 volts combined over-current inputs (active = pulled low)
    4. awm-124 pin 1 21v AC power on signal
    5. awm-124 pin 2 -50v dc negative -7v bias for protect chip
    6. awm-124 pin 9 +13v dc power for protect chip
    7. awm-124 pin 10 +65v dc power for relay

    and then to complicate matters, there is C1, which when IT fails, while the relay gets HOLDING current (q2 conducting), because of energy conservation measures (R4 470 ohms and R15 1600 ohms), there ISN'T ENOUGH current to PULL the relay IN, C1 allows an extra "kick" of current by temporarily bypassing R15 1600 ohms to pull the relay in.
     
    Last edited: Jan 1, 2015
  9. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    About test parameters for q2 and pin values:
    a) Even though there is no longer a click and then sound (no output to speakers)... should I have speakers connected?
    b) What is the state of the A & B speaker buttons?
    c) Is the volume still turned down?

    About test parameters for DC offset:
    a) Is "at the speaker terminals" the same thing/place as instructed by tsd71? (terminal 10)

    Thank you for all your help.
     
  10. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    I found the test parameters for the DC offset on page 25 of the manual, so I'm good there.

    Now when I check pin 10, I read 0.9 volts and cannot change it in the slightest by adjusting VR2. (both left and right channels show 0.9v, I did not attempt to adjust R2 on the right channel)
    Shall I proceed with cutting the (blue) jumper wire? Why would this wire even be there?

    The manual says to turn VR1 fully clockwise but I did not touch either one... should I do that too?
     
    Last edited: Jan 1, 2015
  11. Watthour

    Watthour Electron Rancher - JS3600

    DY - Perform the measurements with no speakers connected. If the protection relay is not closed, the amplifier section will not be connected to the speakers anyway. As a result, the speaker selector switch positions are irrelevant.

    Keep the volume at the minimum position.

    For measuring the offset voltage, connect to Pin 5 of the protection board (AWM-124) for the left channel and Pin 8 for the right channel, and use a chassis ground as the reference (common) point.

    Do not adjust the trimmer (VR1 on AWH-073) with the power connected just yet. It might be a good idea to drop some cleaner onto the trimpot wiper and exercise it with the power off, but be sure to return the trimmer to the same relative position after cleaning.

    The wire jumper is installed to shunt a "spare" resistor in the circuit. The normal circuit design is such that normal adjustments should be able to achieve the desired offset with the wire intact. The factory recognized that if several of the components were on the edge of acceptable tolerance, the normal design would be insufficient to control offset and additional resistance would be needed to allow the adjustment to reach the specification. Cutting the jumper wire adds the resistance of R5 to the circuit (an additional 47KΩ) to allow this adjustment. Until the other problems can be remedied, it may be best to keep the jumper intact for now, but report the results of adjustment attempts.
     

     

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  12. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    Regarding dc offset L adjustment:
    With 0.9v value on pin 10 and no change by adjusting VR2...
    a) desoldered one end of jumper wire
    Resulting in no change of 0.9vdc value regardless of VR2 position. Out of curiosity, I checked VR1; it was approximately mid position so I moved it full clockwise, then full counter clockwise then back to mid position with absolutely no effect on 0.9vdc value.

    That said:
    Q2 base = 0.0vdc
    Pin 5 = 0.9vdc
    Pin 8 = 0.9vdc
    Pin 4 = 11.5vdc
    Pin 1 = 60vac
    Pin 2 = 0.62vdc
    Pin 9 = 12.5vdc
    Pin 10 = 70vdc
     
    Last edited: Jan 1, 2015
  13. markthefixer

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

    Messages:
    21,118
    Location:
    Bensenville,Illinois
    measure and post (PLEASE COPY THIS and ADD YOUR READINGS TO THE END OF EACH LINE!!):
    (don't make me work harder figuring out each and every line,
    I didn't type it in to exercise my fingers,
    I WANTED to see it again so I wouldn't have to look it up again
    going back and forth EVERY line while trying to figure out what's wrong)

    power supply awr-156
    awr-156 pin 22 +50v reg
    awr-156 pin 23 +23v reg
    awr-156 pin 25 -23v reg
    awr-156 pin 27 -50v reg
    awr-156 pin 28 -13v zener
    awr-156 pin 16 +13v reg

    DO NOT BE FOOLING AROUND WITH ANYTHING UNTIL ** I ** TELL YOU. (edit - especially the next post's pin awh-073 pin 2 foolishness, sorry watthour :tears: )
    This is an EXPLORATORY PHASE.

    I had one guy (this week!!) in exploratory phase who started twisting pots when tired - willy nilly, he THOUGHT he was following the manual - he BLEW OUT HIS GODDAMN AMP!!!!
    The readings and pots weren't responding as he expected, so he blindly bulled on ahead.
    Things like that (not responding) MEAN THINGS TO ME DAMMIT!!!

    HE went full clockwise and counterclockwise TOO!!!! BLOOIE!!!!

    You are a blind man in a mine field asking me (the guy with the map) to guide you out. Then you start wandering around on your own...
     
    Last edited: Jan 1, 2015
  14. Watthour

    Watthour Electron Rancher - JS3600

    THAT might be a problem. Something is likely awry in one or both of the power amps.

    Further checks should be done with NO speakers connected and at minimum volume, no signal input.

    It might be good to isolate the two channels by desoldering the connector pin at Pin 2 on one of the AWH-073 boards. The same can be done by lifting a jumper on the amp board if you study the board artwork.

    That may help identify which of the two channels (or both) is responsible for the excessive sense voltage at Pin 4 of the protection board.

    EDIT: MTF finished before I did - Follow his suggestions FIRST.
     
    Last edited: Jan 1, 2015
  15. markthefixer

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

    Messages:
    21,118
    Location:
    Bensenville,Illinois
    awm-124 pin 4 is fine, it is pulled LOW off board to signal overcurrent condition, and it has to be high to be pulled low. R3, 10k to +13v does this. With base limit resistor of R2 (13k) and voltage protection diode/current steering D2.

    DONT PHUCK around with the amps (awh-073 pins 2)- you will only have to undo what you have done and will do.

    The DC offset AIN'T the amps FAULT!! Garbage in - garbage out...

    BOTH amps showing the same inappropriate DC offset means LOOK at the power supply.

    awm124 Pin 2 SHOULD have been -50v - the -50v regulator is zorched... and I'm looking for MORE damage...

    If you had left the DC offset pots alone, once we fixed the -50v supply, it would have been a minor tweak to adjust the DC offset to compensate for the slightly altered voltage of the repaired -50v regulated power supply.

    watthour - sorry about yanking yer chain, I'm a mite testy this morning - I lost a $140 gamble with a 39" ccfl lcd tv last night/this morning, wouldn't light up, bought it for $100, spent 40 on extra supply board and inverter board that arrived in the nick of time before new year's. FORCED the psu and inverter on last night and found a cracked screen :tears: . must be something in the digital board pulling down a supply, but since I discovered the cracked screen, it isn't worth pursuing...
    I MIGHT feed +5v at 20 amps or so to it to watch the short blow itself off the board... for entertainment
     
    Last edited: Jan 1, 2015
  16. Watthour

    Watthour Electron Rancher - JS3600

    [hijack]

    Ouch, Mark. A good flashlight may have been able to reveal that cracked LCD, but I know it's too late now. You're right about the value - A replacement LCD isn't going to be economical at all. I've done many in laptops and smaller monitors, but the big ones are just too $$$. Maybe you can at least recycle the CCFL driver and lamps.

    [/hijack]

    Thanks for the education on the amp overcurrent signals. I was apparently over-generalizing from past experiences.
     

     

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  17. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    power supply awr-156 instructions

    power supply awr-156
    awr-156 pin 22 +50v reg = +50v
    awr-156 pin 23 +23v reg = +23v
    awr-156 pin 25 -23v reg = +0.65v
    awr-156 pin 27 -50v reg = +1.5v
    awr-156 pin 28 -13v zener = +0.65v
    awr-156 pin 16 +13v reg = +13v

    I did not mean to upset you. I have a Manufacturing Engineering background and understand the importance of having a process to follow and when troubleshooting (effectively) only 1 variable at a time.
     
  18. Watthour

    Watthour Electron Rancher - JS3600

    I don't think you upset Mark. I'm guessing, as he replied, that the frustration of the LCD fiasco rubbed him the wrong way.

    Yes, logical half-splitting, sequence, and analytical process can be critical, just as you know.
     
  19. danyost

    danyost New Member

    Messages:
    16
    Location:
    Perris, California
    Hi Mark.
    I'm not doing anything until I hear back from you.
     
  20. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

    Messages:
    4,903
    Location:
    Las Vegas Nevada
    Start a Mouser order for the Power supply caps and transistors while waiting for MTF.
    What's your intentions for the set?
     

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