SX-1280 Tuner issues

Discussion in 'Pioneer Audio' started by xratedpez, Mar 27, 2013.

  1. xratedpez

    xratedpez Super Member

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  2. bktheking

    bktheking Gitter Done!

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    I should buy that kit, BTW i'm going to watertown in a couple of weekends to stay for a couple of nights, we should grab a beer.
     
  3. markthefixer

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

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    I posted about alignment tools several times in the past, I'll see what I can find.

    Plastic hex, one end undercut, both hex ends are ~0.075 inch or 5/64 or ~2mm
    THIS is an EXACT dead-nuts on number, I took out my tools, and ran through a crapload of Pioneer tuner boards I have here, checking against the fit of the coils that use the hex tool, and then I took out a micrometer and MEASURED across the flats (3 measurements per hex, one on each flat) on both ends to arrive at the size.

    GC 9302
    GC AS 9302 (anti-static)
    maybe 8284




    http://www.gcelectronics.com/order/SubCatPDF/alignment tools Kits 380-387.pdf
    This is the GC "catalog" which I suspect has plenty of errors, from my experience with their tools versus what I just read in it....

    which means the 9302 numbers were based on the catalog, while memory and other sources suggest that the 9300 and 9301 numbers may also be appropriate. NOTHING SOLID tho, that I can point to.





    The place I got mine is long out of business.
     
    Last edited: Apr 21, 2013
  4. xratedpez

    xratedpez Super Member

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    Ok- the undercut end of GC 9300 is indeed the right tool here it appears.

    Whilst going through your directions several posts ago Mark, I now realize that the tuning meter doesn't move at all, FM or AM. It is always centered. I didn't make any core adjustments.
     
  5. xratedpez

    xratedpez Super Member

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    Wish I could, brother- wish I could. Bachelor party in Atlantic City that weekend, which really doesn't excite me considering my layoff two weeks ago. Interview tomorrow; hopeful but don't want to get too excited.
     
  6. markthefixer

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

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    tuning meter never moved....

    you wouldn't have happened to notice if the signal strength meter budged as you tuned across the spectrum?

    I gotta start asking more basic questions.... sigh...

    hang a dmm across the two tuning meter terminals.

    move the bottom core slightly and see if the tuning meter moves or the dmm gets a reading other than almost zero.
     
  7. xratedpez

    xratedpez Super Member

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    Signal strength meter moved, yes. Will try your suggestion and report back.

    Remember... I've not worked on tuners before and am learning by following your directions. Please be patient.
     
  8. xratedpez

    xratedpez Super Member

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    Tuning meter moved. I then jumpered the antenna strip (and strap) and adjusted the tuning meter back to zero on a dead FM channel.

    Still no FM movement of signal meter, and no audio.
     
  9. markthefixer

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

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    Ok, yes I gotta remember... better directions.

    Basically now we gotta figure out if the TA7xxx? IF amplifier chip is being fed an IF signal from the front end tuner - the ability to adjust the center on a dead FM means that the detector chip is working... good...
     
  10. rcs16

    rcs16 Super Member

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    Hi Guys,

    Obviously, one or more chips/transistors have popped due to the hi-voltage fault.
    Gotta scope the signal from RF in to IF etc, so the proper way is to apply a good signal from a sig gen and trace it through.
    I could offer to give it a shot at fixing it , assuming that if one of the special IC's are gone I can find them.
    Could unsolder the IC and socket them, so it will be easier to change, one or more will have to be done anyways.
    Too bad they did not stick with the ole HA1137. Sounds like a real pain to get it out, especially if it has those wire wrapped connections, but I have done this before.
    Might think of sourcing some spare parts off an old tuner in the SX-?80 series as they are the only ones using those PA-? parts.
    Their is the detector, mute(This one is the one that hard to find) , PLL stereo ics the Toshiba IF chip but if is bad & can not be found, you can figure out a way to use the HA1201, just refer to the other tuners in the sx-?80 series.
    I should offer a kit to replace these old tuners with a electronic tuner :) Remove the center tune mtr and replace with a 7 segment x 4 Amber LED and replace the flywheel with a encoder, it is really that simple, with a MCU. Might do this with a current hacking of a Sansui G-7500 (Piece of crap) and putting in a SX-1250 transformer plus a TI LME49830/Exicon Lateral FET PA.
    Good luck mate.
    Rick
     
    Last edited: May 1, 2013
  11. bktheking

    bktheking Gitter Done!

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    Just a little update on this thread- I worked with pez and had him trace with the scope, pa3001-a was infact working and passing signal to PA1001-a. We then traced out the MPX chip to 1002-a and nadda. Found a chip, he installed it today and it's now passing signal out to 1002-a but as you could guess, 1002-a is shot- all pins are pinned at ~13v, now comes the real challenge.

    Cheers.
     
  12. tsd71

    tsd71 RIP Tom Petty Subscriber

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    Excellent work KING!
     
  13. bktheking

    bktheking Gitter Done!

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    Thanks-

    1002-a, the challenge, I found an equivalent found in the hk 715, just as rare, known as kb4438- it's a dual op amp chip with negative feedback in/out and built in muting control. I'm still looking through the long list of fm chips hoping to come up with something.
     
  14. rcs16

    rcs16 Super Member

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    Really now!! and you are sure it is the same part as Pioneer has used?
    Try contacting Pioneer, to see if they can still sell the part?
    Internals of the mute chip? The lesser pf the Sx-?80 series do not even use this mute chip?
     
  15. bktheking

    bktheking Gitter Done!

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    sx980 and up and yes i looked at both implementations. Its my understanding that toko made the chip, pioneer didn't sell the chip to toko, im thinking it was the other way around. Toko also makes coils and whatnot for fm tuners.

    http://diagramas.diagramasde.com/audio/HK715 sm.pdf

    page 22 of the pdf shows a block diagram of the 4438 chip, a few pages down is in circuit.
     
  16. markthefixer

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

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    Well I can confirm that Toko made the KB4437 chip and that it's a substitute for the Pa1001a stereo decoder chip, both by reference:
    http://www.audiokarma.org/forums/showthread.php?p=4935061&highlight=kb4437#post4935061
    http://www.audiokarma.org/forums/showthread.php?t=455425

    and by actual experience, that's a Toko KB4437 chip in a PA1001a position on a SX-1980 tuner board that works correctly.
    [​IMG]

    Looking at the diagram in the PDF for the 4438 does strongly resemble a redrawing of the pa1002a internal diagram:

    [​IMG]

    [​IMG]

    (more to come)
     

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    Last edited: May 4, 2013
  17. markthefixer

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

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    The point where I was at, not much else could be done with no signal coming out of the FM detector chip.

    and a probable dead FM front end. NOT something that would be fixable over an internet forum.
     
  18. rcs16

    rcs16 Super Member

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    Good fact finding on that mute chip, finding its origins.
    So can you source this IC? & does it solve the problem?
    Why not just bypass it for now? it maybe shorting the O/P of the stereo de-mux? and no muting & de-emph okay but you should still get sound and prove that this is the culprit.
     
  19. bktheking

    bktheking Gitter Done!

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    I'm trying my best to find a replacement, not going to to be easy.
     
  20. markthefixer

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

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    Back burner project of mine, a plug in replacement. Looks like some op amps, timing circuits and muting circuits. Been collecting info and investigating for 2 years, slowly showing progress.


    You CAN get the tuner singing by just duplicating the sx-880 circuitry from the pa1001 outward. That was my first intent with MY sx-1280 with a dead pa1002a....
     

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