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SX-1250 right channel "WHAP" speaker distortion

Discussion in 'Pioneer Audio' started by Eagle1, Oct 4, 2008.

  1. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Not the speaker as I have already interchanged HPM-100's to troubleshoot. The problem is alway on the right channel so it's isolated to the 1250 right channel. It occurs with the volume up to around the 10:30 or better (-28 db) on CD's and LP's even with the low filter engaged. Turn down the volume and no problem. What board should I start looking at first? I'm guessing some caps are going south as I never really had a problem before but all are original. On another note that might help to solve this the right side heat sinks are a bit cooler than the left side ones. Both seem to coincide with my new problem. ?????????????????
     
  2. EchoWars

    EchoWars Hiding in Honduras

    Messages:
    28,783
    Location:
    Kansas City
    The receiver needs to be benched, with a signal generator, a dummy load, and a scope. Sounds a little like it might be some sort of early clipping, maybe due to a missing regulated voltage (to that end, check the +/-65V regulated outputs).
     
  3. slow_jazz

    slow_jazz AK Subscriber Subscriber

    Messages:
    13,887
    Location:
    SE Michigan, Downriver....
    For starters I'd try a separate pre-amp and see how it sounds. Just unhook the jumpers and hook the preamplifier into the power amplifier connections. If it sounds good it's the Pioneer preamplifier section giving you trouble. If not it's the power amplifier section giving you trouble. Then you can go from there. Also remove the bottom panel and see if the big 4 capacitors are leaking.
     
  4. EchoWars

    EchoWars Hiding in Honduras

    Messages:
    28,783
    Location:
    Kansas City
    Yeah, I guess narrowing it down to the amp or preamp would be a good idea. I was assuming an amp or PS problem.
     
  5. markthefixer

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

    Messages:
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    Location:
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    Once you do the pre/power jumper thing ( a QUICK test is to swap the left out to the right in and vise-versa), measure the DC and AC voltages across the terminals of the four big power caps. Then post them. If the AC voltages are larger than the DC voltages, you need to put a 0.1uf 100v (or greater) capacitor in series with the cheap meter you are using.

    The presence of four caps means the unregulated power to the output transistors is split, with separate left and right power, thus a fault in one wouldn't affect the other.

    Next you need a manual, first to find the +65v and -65v regulated voltage measuring points, but those voltages are shared by BOTH amplifiers.

    Then you need to measure the dc offset at the outputs of the amps, and also check the idle current.

    If it is DC leakage, the preamp has to be leaking DC and the amp ALSO has to have leaky caps.
     
  6. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Thanks for a good starter tip. I have a Sansui 5000X that I just brought back to life that I can use for the first test. From there I can on to step two and check voltages. I have the service manual and Goat67 has all the test equipment to dig into further. He's been bugging since day one to recap and adjust so this wouldn't happen. He one another bet! Thanks all for the info and I'll post as I go along.
     
  7. Fred Longworth

    Fred Longworth audio fanatic

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  8. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Update

    Tried the same circumstances this time without the HPM-100's but just my JBL E100's same CD that produces the problem. Powered up with vol. down and brought it up to the same clip level that the 100's produced. All went silent. Turned down the volume and shut down. Powering up and using FM or CD no sound from A or B speakers, not both pairs at the same time! So something failed. Receiver powers up and goes out of protection mode, I hear the click. Good thing I hope. I'll be puting on the bench later in the morning tomorrow and pull the cover hoping it might be a blown fuse. I know that it's a start but something finally gave up the ghost and failed, hopefully it'll give some sound output and will be able to go from there. Doesn't sound like a capacitor problem unless it leaked voltage to a transitor or two???
     
  9. slow_jazz

    slow_jazz AK Subscriber Subscriber

    Messages:
    13,887
    Location:
    SE Michigan, Downriver....
    Usually with the 1250 you turn it on and after 3-4 seconds it will click and be ready to go. Do the front panel lights come on??
     
  10. markthefixer

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

    Messages:
    20,494
    Location:
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    The first, IMMEDIATE click is the soft start, several seconds later is the protection circuit deciding everything is ok, and connecting the speakers.

    Do you have the manual YET? If not, get one, you can download it from the database.

    Do you have a DMM and know how to use it?

    If so, we check the unregulated and regulated voltages first, then we check the amplifier output voltages. I can direct you to where and how...
     
  11. goat67

    goat67 AK Subscriber Subscriber

    Messages:
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    Location:
    Twin Cities MN
    Mark
    I will be assisting Eagle1 on the repair he does have the SM and I have a fluke DMM that we will be using I also have a Tek scope A Signal Generator and a Distortion Analyzer hopefully we will not need anything more than the DMM. We will be following your lead all the way.
     
  12. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Mark,
    I get both the first click and 4 secs. later the second click. All lamps and FM meters work. As Goat67 stated I have the SM bound hard copy and electronic versions and I'm glad he'll be helping me out with this. He knows how much I like this baby and how long it took for me to find it along with the HPM-100's. We both knew this day could happen, but I was being an optimist. Thanks for everyone's support during this.
     
  13. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Dumb Ass award

    I guess I deserve this award, thanks to Goat67's eyes. When I pulled the hard jumpers from the receiver and installed my jumpers I decided to try out the JBL's first which put the Pioneer into protect. Then I replaced the jumpers with the originals jumpers but put them in the adapter connections not the pre/amp which are a bank above. Lighting and access are my defense but shouldn't be. Goat67 noticed my error while it was on the bench not in the stand. Hooked up a pair of speakers and we had music. But clip on the right side still needs to be addressed. We took voltage readings of the AWR-106 board and A/C voltages off of the main caps. I'll post our readings later once my ears come down to size. For now the big caps need to be replaced and I'm sure the caps on the regulator board. My stupid mistake but better than loosing something worse! :sigh:
     
  14. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    measurements

    Now that I'm done kicking myself here are the voltage measurements Mark.
    AWR-106 board:
    Pin 1 = -69.0
    Pin 2 = 69.0
    Pin 6 = 83.85
    Pin7 = 22.78 to 22.85
    Pin 8 = 5.37
    Pin 9 = 13.29
    Pin 10 = 25.37
    Pin 11 = 66.1
    Pin 13 = -66.15
    Pin 14 = -24.73
    Pin 15 = -85.9 to -86

    Four big 22,000mf caps looking from the front:
    Lefts: 68.3, -68.3
    Rights: -69 to -69.2, 69.3

    And there is quite difference in the big heat sink temps, the right side is definitely cooler than the left side.
    Thanks
     
  15. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    How do these voltages look? The Cap volts look to be high, I believe they should be +65v and -65v? The AW-106 measurements look like they might be in tolerance except pins 1,2 and 15. Waiting for advice before ordering parts. Thanks
     
  16. markthefixer

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

    Messages:
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    Location:
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    I think that all the voltages are fine so far.

    Now the offset voltages and idle current need to be checked for each amplifier channel.
     
  17. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Adjusted the offset and bias voltages within +- .2mv. Stabilizer voltage was at +66v & +66v. Aligned them back to +65 &-65v and had to readjust the bias because they dropped just a bit. DC offset was within .5mv before we made adjustments. We let it stabilize and watched and both sides held pretty steady as long as we didn't walk by the bench. (dual meters) We did run into a bad connection on the right amplifier board that gave use some grief but fixed it before going on. Loose female connection was at fault on the plug end. With all of the settings set to spec without a load both sides are now pretty even in temp. Even so I'm still getting clip on the right channel bass driver with the HPM-100's at -28 db but not the left speaker. Switching speakers produce the same results. Switching to the JBL's no clip at above settings. But if I try both sets of 8 ohm speakers and go past -28 db the circuit protect kicks in. Looking at the boards, the CP board has some visable/questionable caps that will need to replaced. But this still doesn't explain why I'm getting bass clip on the right channel and not the left.

    My Sanui 5000X rated at 60w kicks ass paired with the HPM-100's compaired to th SX-1250. And this was a dust ball that I cleaned up that I got from Retro. Clean sound and great mids. I know the SX-1250 is more up to the challenge with a bit more work.
     
  18. markthefixer

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

    Messages:
    20,494
    Location:
    Bensenville,Illinois
    Sounds like one of the output transistor set isn't carrying the load, or is damaged.

    Check the individual emitter resistor voltages (across each resistor) to see what the individual transistor currents are, and post them.

    The pin 7 to pin 19 reading for setting the idle current is a composite of all 4, we need to look at all 4 individually.

    (Just in case, those are the four 0.5 ohm resistors on the amp card, at the corners close to transistor cable sockets)

    You will probably want to replace the other 7 or so with OnSemi MJ21193G and MJ21194G.
     
  19. Dudeman

    Dudeman New Member

    Messages:
    4
    Swap power amp boards and let stabilize(warm up for 30 minutes) readjust bias E and idle I. Try your operational test for clipping again and see if it follows the board. If not you do have a final transistor(s) failing. Not suprising as your pushing those old boys.
    -28(loud) shotgun the transistors on the side that is in question. If it does follow the power amp board the .5 ohm's are a good start.
     
  20. Eagle1

    Eagle1 Super Member

    Messages:
    1,190
    Location:
    Inver Grove Hgts, MN
    Thanks, we'll check emitter resitor voltages and post.
     

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