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Another SX-1250 protection problem

Discussion in 'Pioneer Audio' started by SaturationPt, Jun 14, 2017.

  1. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    Reading about SX-xx50 protection modes here will make your head spin. Even just SX-1250 there are many, but none exactly like mine.

    This is a bit different. First the symptom:

    Turn it on, it will play fine for an hour, loud or soft, Pink Floyd or David Benoit, then go into protection. It will come back out after a few seconds, then back into protection. The cycle will repeat with a decay in play-time, until it stays in protection.

    Turn off, let it sit for a couple of hours and the cycle will repeat: long time before the first time it goes into protection.

    Now the history:

    This is a favorite old piece of mine, has been in storage, but my current use-it-or-sell-it mode has me pulling things out to see if I still like them enough to keep. I pulled it out a month or so ago, opened it up, checked the Power Amplifier board voltages and Stabilizer board voltages per the manual and all was fine, so I put it in service.

    I decided I like it enough, but the shrink-wrap on a couple e-caps on the power board is receding so I figured it's time to go through it. I spent a few days going through Mark's list here and the schematics, decided to start with restoring the PS board, Stabilizer board, and Power Amp boards so I ordered the parts for these boards (all caps and semis). Not installed (yet).

    When the trouble started, I put it on my bench, checked the same voltages mentioned above, all still stabile. I pulled the amp boards and replaced C11 and Q11 on both boards hoping for a quick-fix so that I could go back to restore mode. No joy, same failure, playing quietly on my little bench 2-way speakers.

    It played fine for a couple of weeks before this started. My speakers are efficient 8ohm JBLs and I don't run it hard, nothing in the receiver appears to be getting unusually warm and both channels were running about the same temp. I have also gently freeze-sprayed the semiconductors on the PS board and stabilizer board after failure to see if this would quickly return it to operation, no change. Seems more like a cap is breaking down and it takes some time to "reset" to the long-play point again.

    Finally, my question:

    I'd like to repair before restore, ... if I can. OTOH, if a restoration using the parts that I have already bought and plan to install will resolve the problem, ... it does avoid that pesky troubleshooting phase.

    So does this failure mode look familiar enough to anyone that you can point me directly to a measure and repair?

    Should I just rebuild the power and stabilizer boards and see if it is now happy?

    Thanks to anyone who spent the time to read this far, and especially (in advance) to anyone who has a solution for me.
     
    Last edited: Jun 15, 2017
  2. markthefixer

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

    Messages:
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    Location:
    Bensenville,Illinois
    This will be an incremental fix, because it is possible that the protection is operating correctly and something is going wrong to cause it to want to go into protection.
    IF you are willing, we can trade troubleshooting for (delayed - but eventually....) parts replacement.
    But due to my online timings, the troubleshooting will be a slow cycle.

    The cycle timings - the time part spent IN protect - are important - we are looking to see if the protect circuit is violating the "power up time delay". If it isn't, then it isn't the relay drive transistor, and something else is causing a genuine protect.

    first thing - freeze spraying the power supply - nah, freeze spray the Q5 2sc1166 relay drive transistor on the protect board, up top of the board, the transistor closest to the relay... (nice that it's easy to access)

    restoration order:
    protection board
    (power supply rebuild optional at this point - but I would do it even if it didn't address an immediate failure)
    power amp boards protect function parts C11 and Q11
    power amp board in general.

    each of these lines also represents a stopping point to re examine the progress in curing the fault.

    Quite frankly, the rebuilds are so quick I generally just do the four boards at one fell swoop and be done with it. I spend more time cleaning them afterward (and during - on the component side).
     
  3. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    I understand the cleaning and R&R part consuming enough time that it probably isn't worth pulling the boards twice (once to repair, then again to replace parts), but there's part of me that hates "part-swappers" who masquerade as technicians, ... which I'm already skirting since I replaced C11 and Q11 without measuring anything significant.

    Anyway, freezing Q5 has no effect, in fact nothing on the protect board nor the TO-220s on the PS board are affected by the freeze spray.

    Its condition has degraded however, I turned it on tonight to get some measurements, ran about 2minutes, into protect for about 2minutes, played for about 30seconds, back into protect for about 2minutes, played for a few seconds and into protect, ... didn't come back out of protect.

    Letting it rest for a couple of hours will probably reset the failure mode but I'll be in bed by then. I'm pretty sure it'll play for a little while again tomorrow if I ask it to.
     
  4. zebulon1

    zebulon1 Into Phase Linear's lately Subscriber

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    Let us see the pin voltages on the protection board when in protection.
    Pin 2 is AC
    The rest are DC
     
  5. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    All to ground zeb?
     
  6. zebulon1

    zebulon1 Into Phase Linear's lately Subscriber

    Messages:
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    Affirmative.
     
  7. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    Pin Norm Prot
    1 64.5 65.3
    2 7.26 7.22
    3 -24.59 -24.88
    4 .9mv .6mv
    5 16.86 15.5
    6 2.7mv 2.5mv
    7 -1.9mv -.4mv
    8 -1.2mv -.4mv
    9 1.2mv 1.0mv
    10
    11
    12 70.3 70.0
    13 -70.0 -70.0
    14 -.4mv -.4mv
     
    Last edited: Jun 14, 2017
  8. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    The failure mode has again changed however, it is clicking in and out of protection constantly, sometimes in or out in only a second, sometimes in or out for several seconds.
     
  9. zebulon1

    zebulon1 Into Phase Linear's lately Subscriber

    Messages:
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    Location:
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    Good job with the readings.
    Pin 3 should be reading -25v's.
    Something is drawing down the -25v supply on pin 3. Good chances it's in the protection circuit, because it recovers when in protection.
    The rest of the voltages are good, the amps are dialed in as well.

    These voltages are optimum:
    pin 1 +65v DC,
    pin 2 7.5v AC
    pin 3 -24v DC
    pin 5 closer to +20v DC (is good). Or +3v DC if overcurrent triggering (Bad)
    pin 6 0.000v DC
    pin 9 0.000v DC
     
  10. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    Thanks for catching that, and it was a mis-type on pin 3, which I now corrected (was showing -12.59v pin 5, corrected to -24.59).

    I have a different twist for this one. Messing around I have changed the failure mode from the first post to the 8th. That seemed too flaky to me, so I did a little prodding.

    Light pressure on the protection relay changed the output, indicating what I thought was a bad solder joint on the relay. I re-soldered all of the joints on the board and re-installed. Odd, pressure on the relay (plastic housing) still makes channels cut in and out. Maybe a bad trace, I don't see one, ... but if the relay is bad and has a high-resistance contact, will this trigger the protection circuit and turn off the relay? I kept pressure on the relay to keep it playing properly and the relay didn't click off again, (it was actually clicking before, not just losing contact).

    Unfortunately the relay was out of stock when I ordered, and the only part that I didn't buy! I'll have to get back on-line and find one.
     
  11. zebulon1

    zebulon1 Into Phase Linear's lately Subscriber

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    Well for sure it's in the protection circuit.
     
  12. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    That's good news of course, thanks for your diagnostic powers!

    At this point it seems best to rebuild the protection board (including a new relay), put it back into service and run it a while to be sure it's healthy before rebuilding the amps and PS boards.

    Still, I've seen many bad protection relay and almost always replace them when I have the opportunity, but they usually simply don't pass signal reliably, I've never seen one that will (apparently) trigger the protection circuit to turn the relay off!
     
  13. markthefixer

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

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    Have you cleaned the connector pins ON the protection board to the chassis (the pencil eraser trick)

    The board has a -24v entry point, with taps of 91k and 10k ohms. it could short to ground or 7.5v ac. Not much else to affect the -24v.

    The turn off of the circuit could just be the coil current being interrupted. Simple as that.
    Don't forget that this board has it's own 65v to 35 volt voltage regulator, something shutting that down could also do it.
     
  14. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    I did clean the pins when I pulled the board to re-solder the relay and other components, I can't say no change but it definitely didn't fix the problem.

    I don't know why the timing is so (apparently) random now, nor why holding my finger on the relay case seems to keep it from clicking into protection, but at this point I agree that the problem appears to be on the protection board.

    Maybe (guessing here) the output from Q5 is weak enough that it's barely holding the relay in, and pressure on the relay is enough to interrupt the contact to the speakers, and this interruption causes some noise that triggers the protection circuit? I don't completely understand what Pioneer is doing in the protection circuit here (more complex sensing than most), is this a possibility?

    Nothing on the board looks like it has been hot (including relay contacts) but I never have much load on the receiver so maybe that's expected.
     
  15. rcs16

    rcs16 Super Member

    Messages:
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    Location:
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    Sounds like a intermittent connection or bad solder joint.
    you can test out Q5 by measuring its terminal voltages.
     
  16. markthefixer

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

    Messages:
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    Location:
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    Hear hoofbeats don't think Zebras...

    I suspect the coil wiring IN the relay. Some pretty thin flying wires. Unusual - but not as exotic as the speculation.

    I have dealt with OOS relays by getting a Plug-In/Solder tab relay and either clipping part of each tab to fit the hole with about a 1/8 inch offset of the relay to one side, and I have also (with a VERY steady hand) converted the holes into slots to fit the pins with a PCB drill.

    653-my4-02dc24 correct relay
    653-MY4-DC24 Plug-In/Solder tab relay

    And in the process of making this post I find that Mouser now has 165 of the correct 653-my4-02dc24 relay.
     
  17. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    350
    Location:
    N.E. Indiana
    I did order the relay from Mouser today, my part order was from DigiKey however, and they are out of stock so I had ordered everything else.

    Funny thing is that I usually replace the relays whenever I'm in this deep anyway, such a common failure and even if it hasn't completely failed I expect that at the age of these receivers the contacts are introducing some noise / resistance to the signal.
     
  18. WE6C

    WE6C Active Member

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    459
    Location:
    Colfax, Northern California
    Make sure when you're pressing on the relay that the circuit board flexing isn't effecting a bad solder joint.
    Bob
     

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