Pioneer SX-580 (or SX-680) No Output due to bad resistor R401?

Discussion in 'Pioneer Audio' started by JamVal, May 26, 2017.

  1. JamVal

    JamVal Super Member

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    1,212
    Found a decent looking SX-580 at a yard sale $5

    To make a long story short, everything seems to work, except no output.
    Cleaned all pots and switches. Made sure ground chassis screws were tight. All fuses are good.
    I don't think the tape monitor switch and/or function switches are the problem (for now).
    I bridged the tape REC / PLAY RCA's and engaged tape monitor and still no output. REC out to another device works. Going from another device to Tape PLAY IN did not work.

    I found an AK thread here where Mark the Fixer said you can try jumping across R401 with a DMM set to DCA.
    I tried it, and I got very good output, equal in both channels. In that thread Mark also said you could temporarily try a metal film resistor to trouble shoot, but a permanent replacement should be a fusible resistor. I'm guessing that's part of the protection circuit since the SX-580/680 has no protection relay?

    The service manual from HiFi engine shows R401 to be 33 ohm, RF1/4PS 000J.
    So I assume that's a 33 ohm 1/4 watt resistor.

    The only local available is a Radio Shack 33-ohm 1/2 watt carbon film. Will that work? or do I need to have a 1/4 watt rating?

    Thanks.
     
  2. markthefixer

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

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    here we get down to the safety aspects.
    The 33 ohm radio shack 1/2 watt carbon film resistor will get you running, but it should be TEMPORARY.
    That 1/2 watt is the sticking point, a lot more fault current will flow before it pops.
    I'm conflicted on this one, because they do NOT use the triangle with the exclamation point safety symbol.
    If they had I would INSIST upon the below:

    RF1/4PS 000J
    The Tuning Fork series ( it has it's own sticky in the forum) TF6 New Resistors and Capacitors (Pt 1) provides the info:
    RF This is a metal film resistor, fusible, with "non-flammable paint".
    1/4 is 1./4 watt
    PS is just plain straight wire, no fancy formed loop
    ... the F for Flameproof is missing !! The RF covers it, I guess
    J is for 5%

    603-FRM-25JT-52-33R @ 0.20 ea at mouser.
    but the shipping will be horribly large in comparison
    so
    go with just a 1/4 watt METAL FILM resistor eventually.
     
    Last edited: May 26, 2017
  3. JamVal

    JamVal Super Member

    Messages:
    1,212
    Thanks Mark, I think I answered my question as you replied.
    Since watts (Power) = I squared (amps squared) x R (ohms).
    The R401 resistor (33 ohm, .25 watt) is designed to take up to 87mA - yes? Referring back to the mentioned thread, Mark the Fixer said anything over 87mA would fry the R401 resistor, so it was designed to not allow more than 87mA, acting like a fuse.
    If I were to sub in a 33 ohm, .5 watt it would allow a higher amperage about 123mA by my calculations.

    So the answer would be no on the 1/2 watt, go with a 33-ohm 1/4 watt resistor? Do I have it right?
     
  4. markthefixer

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

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    correct, all but the metal film aspect of it, as revealed by the tuning fork info.
     
  5. Novice2017

    Novice2017 New Member

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    23
    I also, have a Pioneer SX-580 with a sound problem, but of a different (more strange?) kind: I bought the unit in 1980 and it has been flawless since then (and dust free as well as without any cosmetic damage). Recently, something very strange happened. When I turn the receiver on, the sound (from any source, AM, FM, tape deck, etc.) comes on OK, but within seconds it fades away and never comes on again no matter how long I wait. Within the same few seconds, even if I have the volume control knob in the lowest position (no sound), the two power meters go from 0.01 to 1 and stay at that setting no matter what I do with the volume control knob -- and there is no sound no matter what source I use. When the selector switch is at the AM or FM position, the tuning meter indicates as usual that a station is or is not tuned in; so, it functions normally. Also, when I turn the power off, the power meters jump to their lowest position (left), but quickly go back to about 0.1, and then slowly go down to their power-off position.

    Here is what I have tried:
    1. To rule speaker or speaker wire problem, I tested the speakers on another receiver (the SX-450). No problem.
    2. To rule out a bad contact in the ON/OFF switch, I shorted the switch out. The same problem I described above occurs; i.e., the sound first comes on, but in a few seconds fades away, and the power meters move from 0.01 to 1 and stay there, without any sound.
    3. I treated the volume control potentiometer and the contacts of the ten pins of each of the two power packs with Deoxit. The problem did not go away.
    4. I checked the grounding screws. They are all tight.

    PLEASE, help! I do not know what to do or whether the R401 resistor to which you refer could cause this problem, too. Incidentally, I can find that resistor on the schematic I have, but I do not have a clue as to where this resistor is located on the actual circuit board to short it out and see what happens. Please, don't get too technical in your reply, I am a beginner -- learning fast, but beginner nevertheless! I own a multimeter (measures current, resistance, and voltage both DC and AC), but no other instrument.

    Thank you in advance for any assistance you (or anybody else) may provide.
     
  6. markthefixer

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

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    With the unit ON, find square pin #63 (behind the balance control), (or pin #47 or pin #72) set the DMM to read DC volts (probably 200v scale) connect the black probe to a metal chassis bare point (probably a screw) then touch the red probe to pin 63. You should see minus 22 volts here. It's part of a muting circuit, which your symptoms implicate.

    Deoxiting should be applied to ALL the front panel switches, ESPECIALLY the tape monitor switch - it has some contacts involved with this muting circuit as well.
     
  7. Novice2017

    Novice2017 New Member

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    markthefixer: Thank you very-very much for your speedy and informative reply. I'll try to locate the pin #63 (or the other #s) that you mention when I get home tonight. If the voltmeter reads the wrong voltage, what would that mean; i.e., what kind of repair would need to be done?

    Also, the reason I had not sprayed Deoxit in the rectangular housings of the push-button switches, including the Muting switch, was that I could not find an opening on them. Please, forgive my naïve question, but where should the little tube nozzle of the Deoxit spray can go? Should the front panel be removed for access?
     
  8. markthefixer

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

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    Location:
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    Cart before horse. This will be the first of possibly many readings.
    Don't overthink the plumbing - that's MY job.
    I gotta overthink the directions to taking the readings to eliminate misunderstandings, and get accurate information.
    You'll have enough fun just keeping up with the readings.

    Switches accessed from inside the chassis.They're not buried like in some models.
    Spray in ends on lower part of sliders. BOTH ends.

    Got questions, post PICTURES so I can POINT.

    And now, this should be it's own thread - as it has significantly diverged from the original.

    start by quoting your first post in this thread, to set the baseline.

    also If you have not - DOWNLOAD the service manual, it is an ESSENTIAL road map to components on our journey.
    It would show you that R401 (which I strongly suspect ISN'T involved) is the closest resistor to pin 10 of the board. (by the fuse).
    CAREFUL if poking AGAINST ADVICE there - pin 10 is at POWERLINE potential. (I can't physically stop you from poking around, but I CAN explain the danger).
    I have been known to deal harshly with those that don't follow directions and especially jump (blindly) ahead on their own. Things get busted that way.
     
    Last edited: Jul 11, 2017
  9. Novice2017

    Novice2017 New Member

    Messages:
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    Thank you again so much! No, I won't poke around on my own. I am keenly aware of my limitations and that I may screw things up if I go on my own. I just have been very concerned about imposing too much on your time.

    With a strong flash light, I saw the tiny holes (vents?) on top of the housings of the push-button switches. I used Deoxit in those and at both ends, as you suggested, and worked the switches on and off many times. I also sprayed Deoxit in the other rotary switches that I had skipped before.

    I located the posts with numbers behind the Balance switch. Immediately behind it, from left to right, I found #64, #65, and #66. A bit father back #61, #62 and #63. I measured the DC voltage from ground to #63. It is -22.3V according to a DMM and -21.5 according to an AMM. (The post #63 is connected with a white wire to post #47, which is behind the Bass switch.)

    After the Deoxit evaporated, I tested the receiver again. The original problem persists: As soon as the power comes on, the sound is nice and clear, but fades away in a few seconds, never to come back. Also, the two power meters behave as I had described earlier.

    Please, forgive my ignorance, but I do not know how to start a new thread. I am very new to online forums -- started about a week ago. With help from wonderful postings at AudioKarma, I did manage to fix the flickering-lights-and-static problem of my Pioneer SX-450 and posted (for beginners like me) how I did it here:

    http://audiokarma.org/forums/index.php?threads/pioneer-sx-450-power-switch.700078/#post-10670209

    The cause and solution was different from those described in other postings.

    I downloaded the service manual for the SX-580, and I'll print it out tomorrow. I have also taken pictures of the interior of the receiver and the bottom of the circuit board. If you would like to see any part of it, please, let me know so that I won't overcrowd the site with irrelevant photos.

    Thank you, thank you, thank you for your help.
     
  10. Novice2017

    Novice2017 New Member

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    MarkTheFixer: Poking step #2 = ? As you said, not doing anything on my own. Just... staring at the SX-580's innards every-so-often...
     

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