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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    Did you look for any broken wires? Might be as simple as that.
     
  3. Bradbrews

    Bradbrews New Member

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    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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    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:
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    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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    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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    :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!
     

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