Another SX-1010 this time a transformer

Discussion in 'Pioneer Audio' started by Bradbrews, Apr 5, 2017.

  1. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    The transistors on the sides of the PCB, Q5 and Q6. Do they have a forward collector (KSC1845) when mounted?
    Double check the leg configuration.
    Note:
    The images would be better at a slight angle.
     
  2. loweran

    loweran AK Subscriber Subscriber

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    Location:
    Austin, Texas
    Did you look for any broken wires? Might be as simple as that.
     
  3. Bradbrews

    Bradbrews New Member

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    Location:
    Near Ann Arbor MI
    That's a good point. I did have one on the Control Amp, but I didn't really check every other one. I'll make sure to do that.
    I have to admit that I was feeling pretty confident up until I had no sound.:oops:
    Then I got another boost when I thought I figured it out - that misplaced Q5 - but alas it was not the only thing.
    Here is what the EQ board looks like after rotating Q5 around.
    IMG_3794.JPG
    (I lost my photo editing software on this PC so I can't adjust the exposure..)
     
  4. Bradbrews

    Bradbrews New Member

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    33
    Location:
    Near Ann Arbor MI
    Checked for broken wires, found none. Cleaned up a solder joint that looked poor. Rechecked a few times that every transistor was in per silk screen.
    No sound from the left channel.
    I then switched the pre-outs right for left, and I got sound out of the left channel! Good, at least I know the amp is working in both channels.
    Then I switched from FM to a tape input. Same thing, no sound from the left channel.
    I switched the control amps tone control to Off as well with no change. I'm hoping that means that the whole control board is just bypassed, and that clears that board of a possible issue. Is that true? I guess I better spend some time looking at the schematic to see where to go next.
    I tried to check each transistor on the EQ board in circuit. I was able to get the 0.66X volt number between each one where they were supposed to be, but where I was supposed to read OL, I got 2.xx or 1.xx volts instead, so I suspect to check them they need to be pulled, or at least pull one or two of the legs, right?
    I tried to compare the left and right channels of the EQ boards, but didn't really see much difference, except maybe on the C-E measurement volt value.
    (My Fluke 77 shows V in diode check mode)
     
  5. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    Toasted R13 on the AWG-027 control board?
    The image you posted is hard to tell the leg configurations of the transistors.
    Did you see my last post?
     
  6. Bradbrews

    Bradbrews New Member

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    Location:
    Near Ann Arbor MI
    Yes, but I'm not sure what forward collector really means. I did check that each transistor, especially Q5 and Q6 have all 3 legs going as per silkscreen.
    I'll take some better pictures, and check on R13...
     
  7. avionic

    avionic " Black Knights " Subscriber

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    2SC2240 GR,BL 2SA970 GR,BL BDEnterprise
     
  8. Bradbrews

    Bradbrews New Member

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    Location:
    Near Ann Arbor MI
    Success!
    After spending some time with the schematic, I realized that my tape input test actually cleared the EQ board, and meant the issue had to be in the control amp, or before the pre-in jacks. After a few voltage measurements I was able to determine that the signal was at the output of the control amp at pin 7, but not at the pre-out jack.
    Looking into this one led me to find that the wire on pin 7 was broken inside the insulation, but the insulation was able to withstand a light "tug test" so I wrongly thought that the wire was connected.
    So loweran you nailed it. Once I reconnected the wire, I had sound in both channels.

    On to the deoxit treatment.
     
  9. Bradbrews

    Bradbrews New Member

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    Location:
    Near Ann Arbor MI
    :banana::beerchug::jump:
    Just realizing that I have a completely redone SX1010 in the final stages of the process.
    I promise to be careful when rechecking the alignment of the power amp... No live switching of the mini grabbers!
     
  10. loweran

    loweran AK Subscriber Subscriber

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    Great work man. You will always run into something like this that makes you have to diagnose and do a lot of rechecking and thinking. It can be even worse when you have to diagnose what someone else did to the set before you got in there.

    You are really going to enjoy this receiver. It's fantastic!
     
  11. Bradbrews

    Bradbrews New Member

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    33
    Location:
    Near Ann Arbor MI
    I think I used too many happy smileys.:(
    I finished up - I thought - last night and put everything back together. The new warm white LED's in the display look great.
    IMG_3812.JPG
    The issue is that the Left channel has much lower output than the right, and does not sound as full. I need the balance adjusted way over to the left to get equal volume out of it.
    I swapped the pre-outs again, and the low output follows the left channel, so I know the amps are not the issue. The lower output is on both FM and the Tape In jack. It is present when tone is defeated as well. This leads me to believe that the problem is on the Control Amp board's left channel.
    I'm guessing its in the Q2/Q4 first stage section (if that's the right term) of the board. I do get sound, just not the right volume.
    I probably won't get a chance to open it back up until after Thanksgiving, so I might just have to sit and stew until then...
    My first checks of the pictures of the AWG-027 board do not give up the answer easily, as I have not yet found a part in wrong, but I'll be looking some more at them to be sure.
    A recheck of the wiring that broke and was fixed on that channel is also in mind, as I guess its possible that a loose connection could give me reduced, but not zero output.
    I think I checked the transistors in circuit after I found Q5 on the EQ board in wrong. but now with this outcome, all is in doubt.
    sigh
     
  12. markthefixer

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

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    Just for a quick EASY check, see if going from STEREO to MONO by pushing IN the MONO button
    (between the volume control and the tuning knob) has any effect upon this imbalance.

    If so, it's probably the switches....
     
  13. Bradbrews

    Bradbrews New Member

    Messages:
    33
    Location:
    Near Ann Arbor MI
    Well I checked out Stereo and Mono and it had no effect.
    However, more surprisingly the weak left channel has gone out completely now. In a way, I like this better than the prior problem.
    Now I am hopeful that I'm back to a broken/loose wire. Pin 7 on the control amp was the problem before, and may be again.
    I also fed another pre-out into the 1010's pre-in's and got good sound from both channels.
    I flipped this around just to verify, and the 1010's pre-outs would only feed the right channel. Left is dead.
    Now the wait until after Thanksgiving to dig into it...
     

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