Pioneer sx-550 "sizzles" on power on

Discussion in 'Pioneer Audio' started by rocknroller, Jan 13, 2018.

  1. rocknroller

    rocknroller Active Member

    Messages:
    364
    Upon turning on, lamps flicker and you can hear noise on the speakers **even when just the ground wire of the speaker is connected - No positive wire connected**. This lasts a variable amount of time, usually roughly 5-10 0 seconds, sometimes longer. The audio then kicks in but more often then not, it is distorted. This again lasts for a variable amount if time (5-20 seconds), at which time the light stay on solid and the audio clears up. Once in a (rare) while it will turn on just fine, or the audio kicks in quicker and the flicker clears right up. However 90%+ of turns on result in this issue.
    At first, I thought maybe the large filter caps, but I swapped a brand new pair in and no change. The I pulled the two 4 amp (power board) fuses, no change. Put those back, pulled the two 0.8a fuses which feed the preamp and such, no change. Put those back. Pulled the 1.5a lamp fues, well obviously the lamps stayed out , but otherwise no change. I don't see anything else on the schematic below.

    Pioneer sx-550 power.jpg

    I wonder if the actual AC switch itself could be the issue? Though no amount of wiggling etc resolves anything. I also spray in the area, though didn't see any clear ingress opening for the switch so that probably did nothing.

    Which brings me to my second problem. Once it is all powered up and working fine, the right channel is out. The amp itself is working and there IS audio output at the headphones on that channel, which means it's present at the switch. But there is no output on the A or B right set (or a+b). That switch (which is coupled to the AC switch) was spray but no change. Seem strange/unlikely that both a&B sets on on side would be out but again, I'm not seeing anything on the schematic (below) that explains it other than multiple connection failures there, yet that seems so unlikely to all be on one side.
    Thoughts? Recommended things to check?

    pioneer sx-550 output.jpg
     

     

    Please register to disable this ad.

  2. deltalight

    deltalight AK Subscriber Subscriber

    Messages:
    251
    Location:
    Minneapolis
    Sounds like a defective Power SW or speaker relay. Put your ear close to the Power SW with the volume down in a quiet room and turn the power on. Spraying a Power SW is a bad idea as the contacts should switch dry, not wet.
     
  3. rocknroller

    rocknroller Active Member

    Messages:
    364
    You are correct. I heard crackling, though i couldn't really tell if it was the large AC cap on the power in or the switch since they are both in the same area. Anyway found a hole to spray in and seems to have cleared the cracking up.

    This is take about 5-7 seconds after power on to actually start sounding. Is that normal for this model? I have no reference to compare too.

    There is still the issue of no audio out the speaker selector switch on that right channel. I definitely have it coming in, just not out, regardless of A or B or A&B selected.
     
  4. I LIKE MUSIC

    I LIKE MUSIC Super Member

    General information. This is a common symptom of a bad power switch. Note the fact that the lamps flicker. This is because the power switch is arcing. This arcing can and will damage the switch contacts.

    Cleaning can help, but it may not be a permanent repair because the switch contacts may be damaged.
     
  5. rocknroller

    rocknroller Active Member

    Messages:
    364
    Turns out the switch contacts needed cleaning for the speaker as well, Spraying had done nothing, but when I got a Qtip with alcohol on it and gave it a good scrubbing, it solved it. Good thing because extracting that switch is near impossible and would require what looks like a major disassembly of the unit, including the tuner dial cord stuff which I can never get back together....
    Anyway - All problems solved. Thanks for popping in with the helpful feedback!
     
  6. rocknroller

    rocknroller Active Member

    Messages:
    364
    Also found in the user manual there is a muting circuit of about 7-9 seconds so that's normal for this unit.
     

     

    Please register to disable this ad.

  7. redk9258

    redk9258 Super Member

    Messages:
    1,448
    Location:
    Illinois, close to St. Louis.
  8. rcs16

    rcs16 Super Member

    Messages:
    3,639
    Location:
    Baldwin, Ontario, Canada
    if it is one of those Alps grey AC power switches, then only use the switch contacts to power up a triac or relay. The mod is posted somewhere in this site.
     

Share This Page