SX-1280 Tuner issues

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

  1. xratedpez

    xratedpez Super Member

    Messages:
    1,226
    Location:
    NY
    Folks, this seems to be the last issue with this nice looking unit.

    No AM or FM reception, antenna or not- regardless of muting switch engaged or not.

    Also, when AM is selected, tuning meter pegs. I've lifted one leg of R66 (180ohms) and it checks good. It appears HA1197 (Hitachi) is responsible for the AM section, and it measures near 17VDC on every leg of the IC.

    Other than swapping IC's out (I certainly don't have any spares!), are there other things to look for on the tuner board? The entire unit has now been recapped, and I don't believe the tuner section was tested prior.

    All other threads I've read with these same issues had a number of BAD IC's that were the culprit. I never get components on eBay, but that might be the only option for these legacy chips!?
     
  2. bktheking

    bktheking Gitter Done!

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    17vdc on every pin, that sucker has to be shorted.

    I may have a spare.
     
  3. markthefixer

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

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    SEVENTEEN VOLTS? :yikes:

    It's a THIRTEEN volt power feed. Pin 11 on the HA1197...

    Tuner board pin 23 is one of the power feeds. 13.0v maximum, no higher.

    That high of a voltage may eat chips.

    Let's get the voltage back down, then reevaluate. I'd hate to loose the PA1002a chip, those are a real unobtanium part. I was sweating the tuner of the current bench's occupant and that part for the last day or two. Luckily the problem was off board and didn't affect that chip.

    power supply is three transistors and a zener diode.
     
    Last edited: Mar 27, 2013
  4. xratedpez

    xratedpez Super Member

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    Yikes is right. Pin 11 on the HA1197 measures 17.11VDC and pin 23 on the tuner board measures 16.4VDC.
     
  5. xratedpez

    xratedpez Super Member

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    Mark, you mean pin 23 that goes to the Filter amp board AWM-119? Yep, that measures 16.4V
     
  6. xratedpez

    xratedpez Super Member

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    Getting 16V on the base of Q7, Power Supply board. Something's still awry fer sure.
     
  7. bktheking

    bktheking Gitter Done!

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    I downloaded the manual from akdatabase and I can barely read it lol.
     
  8. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    Try this one here

    That's the hires version. Low Res version is here

    Main site link here
     
  9. xratedpez

    xratedpez Super Member

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    Looking around for a bad resistor on the P/S board... But typically resistors drift UP when bad, correct?
     
  10. xratedpez

    xratedpez Super Member

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    1,226
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    Q5, Q6 on P/S board tested bad. Have a replacement for Q5 on hand, but not Q6.
     
  11. xratedpez

    xratedpez Super Member

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    1,226
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    KSC2310YBU is NLA.

    Any common transistor subs for a suitable replacement?
     
    Last edited: Mar 29, 2013
  12. xratedpez

    xratedpez Super Member

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    Actually, I have a pair of ZTX694B NPN's here... any suggestions there? They seem to match up decently
     
  13. xratedpez

    xratedpez Super Member

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    1,226
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    Popped the Zetex subs in, and now the tuner P/S values are good-- pin 23 is reading 12.8Vm and the voltages on the transistors are normal. :banana:

    Now to determine what's up with the IC's...
     
  14. bktheking

    bktheking Gitter Done!

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    What's it not doing now?
     
  15. xratedpez

    xratedpez Super Member

    Messages:
    1,226
    Location:
    NY
    Same symptoms unfortunately-- no FM or AM sound, AM pegs the signal meter.

    Trying to find some troubleshooting steps for this type of thing, but no luck so far. I don't think I've ever had to troubleshoot a tuner before believe it or not .
     
  16. bktheking

    bktheking Gitter Done!

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    Did you retest the AM chip pins?
     
  17. xratedpez

    xratedpez Super Member

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    I did- they all came out to (roughly) 13.2V.
     
  18. bktheking

    bktheking Gitter Done!

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    Pin 10 is supposed to be ground. What about the fm chips?
     
  19. xratedpez

    xratedpez Super Member

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    FM Chip PA1002 measures 13V-13.3V on most of the pins (as does the AM chip below).

    AM Chip HA1197:

    Pin# / DCV
    1/12.9
    2/12.82
    3/13
    4/13.35
    5/13.35
    6/13.32
    7/12.86
    8/6.24
    9/13.33
    10/ 0.0
    11/13.33
    12/13.35
    13/13.32
    14/13.31
    15/13.33
    16/12.88
     
  20. bktheking

    bktheking Gitter Done!

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    I guess fixing the power supply didn't bring the voltages back down. I'm sure Mark will be along shortly. If you had spare chips to try, well, that would be my first attempt at repairing it.
     

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