Help with FM Signal path circuit debug needed Technics SA-800

Discussion in 'Tuners' started by rocknroller, Jan 11, 2018.

  1. rocknroller

    rocknroller Active Member

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    Actually I think this pioneer sx-550 would be easier? Seems to have the same flow. The proper tie in point would be pin 1 of the HA1137 chip, correct?

    Pioneer sx-550 fm.jpg
     
  2. chazix

    chazix AK Subscriber Subscriber

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    The reading of 1.5V on pin 5 of the AN377 may be significant. I don't read Japanese, but the test circuits in the datasheet have pin 5 grounded. I think that a positive voltage on that pin might be causing the chip to go into muted mode.

    I wouldn't expect that condition to also disable the tuning meter outputs, though, so my intuition at this point is that the AN377 is bad.

    The other advisors in the thread might weigh in with alternative viewpoints, (And they are some pretty heavy hitters, I must say!)

    I can't claim much experience with cross-connecting gear, but I would say that pin 1 of the Pioneer's HA1137 does indeed look like the functional equivalent of the Technics' AN377 pin 1.
     
  3. 39cross

    39cross AK Subscriber Subscriber

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    Edit: here's the AN377 schematic from the the SA-700 service manual. The freebie SA-800 schematic doesn't appear to show the voltages, this one does show the expected voltages. I can check my SA-700 receiver if you need any verification, but based on Dr. Audio's post below, your IC is bad.
    Also, just to note the schematic appears to be incorrectly labelled, the 'meter level' and 'muting level' labels should be flipped.
    AN377-SA700.png
     
    Last edited: Jan 14, 2018
  4. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    The IC102 should still work with 10V on the supply. There is a resistor in series with the supply pin, R115. I bet if you measure on the input side of R115 the voltage will be closer to 12V. If so, that's another indication IC-102 is bad and drawing too much current, dropping the voltage across R115. I think the fact that you could see the signal on pin 1 of IC102 changing when you tune the dial, and that pin 8 has a lower signal level pretty much clinches it, IC102 is bad.
     
  5. rcs16

    rcs16 Super Member

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    I think you could ground the input of CF1 and injecting the signal between F1 and F2 would be easier imo.
    the Hitachi HA1137 and Panasonic AN377 are similar in function and specs from the same era.

    if you measure DCV across R115 and divide by the R value you can calc the bias I and compare against the data sheet spec.

    Agree, rather moot point as too doing the cross injection testing, but it is something you can try as a learning experience if you so choose to learn more about tuner troubleshooting. I have used this technique to even troubleshoot HP RF signal generators and other gear. Nothing better than having the same working unit to compare against.

    Good luck
     
  6. rocknroller

    rocknroller Active Member

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    Looks like from 39cross's voltage schematic post, the 1.5v is normal.
     
  7. rocknroller

    rocknroller Active Member

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    Very helpful for when I get a new chip in - Thanks!
     
  8. rocknroller

    rocknroller Active Member

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    You are correct - 12.9V on the other side of R115
     
  9. rocknroller

    rocknroller Active Member

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    2.5V across R115
     
  10. rocknroller

    rocknroller Active Member

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  11. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    Get the ones from Ceitron. they have been around a long time and seem to be reliable. I doubt anything internal killed that IC, it might have had a ESD hit or powerline spike. If that's the case there may be more damaged ICs. In the days when this was built there was little knowledge of proper ESD precautions in manufacturing, so the IC may have had some latent damage that caused eventual failure or a wire bond could have let go.
     
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  12. rocknroller

    rocknroller Active Member

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    Chip came. Installed - worked great!! Thanks to everyone for the input/feedback/recommendations!
     
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  13. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    Glad we could help! Sort of like telemedicine for audio equipment!
     
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  14. 39cross

    39cross AK Subscriber Subscriber

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    telemedicine by a real doctor...dr*audio! :)
     

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