1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

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

    Messages:
    395
    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
     

     

    Please register to disable this ad.

  2. chazix

    chazix AK Subscriber Subscriber

    Messages:
    1,162
    Location:
    Groton MA
    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

    Messages:
    937
    Location:
    Beverly, MA
    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

    Messages:
    18,780
    Location:
    Cleveland, Ohio
    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

    Messages:
    4,070
    Location:
    Baldwin, Ontario, Canada
    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

    Messages:
    395
    Looks like from 39cross's voltage schematic post, the 1.5v is normal.
     

     

    Please register to disable this ad.

  7. rocknroller

    rocknroller Active Member

    Messages:
    395
    Very helpful for when I get a new chip in - Thanks!
     
  8. rocknroller

    rocknroller Active Member

    Messages:
    395
    You are correct - 12.9V on the other side of R115
     
  9. rocknroller

    rocknroller Active Member

    Messages:
    395
    2.5V across R115
     
  10. rocknroller

    rocknroller Active Member

    Messages:
    395
  11. dr*audio

    dr*audio Fish fingers and custard! Subscriber

    Messages:
    18,780
    Location:
    Cleveland, Ohio
    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.
     
    chazix and rocknroller like this.

     

    Please register to disable this ad.

  12. rocknroller

    rocknroller Active Member

    Messages:
    395
    Chip came. Installed - worked great!! Thanks to everyone for the input/feedback/recommendations!
     
    rcs16 and 39cross like this.
  13. dr*audio

    dr*audio Fish fingers and custard! Subscriber

    Messages:
    18,780
    Location:
    Cleveland, Ohio
    Glad we could help! Sort of like telemedicine for audio equipment!
     
    rocknroller likes this.
  14. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    937
    Location:
    Beverly, MA
    telemedicine by a real doctor...dr*audio! :)
     
  15. rocknroller

    rocknroller Active Member

    Messages:
    395
    OK - Now i'm going to resurrect this thread (though maybe should start a new one) for a similar model (Technics SA-200) with a similar issue. Again, no FM audio at all (no static either, mute off). AM ok. Was hoping it was the same an377 chip issue but symptoms appear to be different in this case and wondering if the problem might be further down the line at the AN363 chip instead.

    At the AN377 chip, there is a signal on my 15Khz scope going into pin 1 and a much larger signal at pin 8 (unlike my previous unit where the pin 8 was much lower). Audio from audio tester on pin 13 (loud, but not particularly clear) and pin 12 (much more attenuated and muffled) Schematic pin voltages are near impossible to read but I noted my readings below. Believe the blue noted ones are ok. The red values all vary based on tuning.

    At the AN363 chip, there is a scope signal at entry Pin 2 that varies with tuning. Voltages at pin 8, 12 and 16 of concern. Not sure what else to check for at this chip. At some point, signal goes to 19kHz and out of range of my scope.

    AN377.jpg

    AN363.jpg
     
  16. dr*audio

    dr*audio Fish fingers and custard! Subscriber

    Messages:
    18,780
    Location:
    Cleveland, Ohio
    A scope with a bandwidth of 15KHz is less than useless to work on rf and almost useless for audio. You need to get a 100mHz bandwidth scope. Pins 4 and 5 are the audio output. What do you see there with the scope? Does the tuning meter show a signal, and does the stereo light come on?
    upload_2018-3-30_23-17-9.png
     

     

    Please register to disable this ad.

  17. rocknroller

    rocknroller Active Member

    Messages:
    395
    Tuning meter shows a signal. Stereo light never comes on (but is a good light).
    No audio with audio tester at pins 4/5 and looks to be some sort of very simple sine wave on scope (both pins). No obvious audio activity at all (dial stationary or moving)
     
  18. rcs16

    rcs16 Super Member

    Messages:
    4,070
    Location:
    Baldwin, Ontario, Canada
    Still working on tuners :) Good stuff guys.
     
  19. rocknroller

    rocknroller Active Member

    Messages:
    395
    Opened up the wallet and picked up a working tek 100Mhz scope. Far exceeds the value of this unit but hopefully will come in handy over the next many years.

    Now with scope in hand - What should I be checking for at AN377/AN363?
     
  20. rcs16

    rcs16 Super Member

    Messages:
    4,070
    Location:
    Baldwin, Ontario, Canada
    Looks like you have good audio out of AN377 and into AN363 pin 2. need to make sure the VCO as part of the PLL is oscillating correctly.
    If the voltages on the AN363 are wrong against the schematic and the data sheet, then it is probably this part, but you have to make sure it is not one of the passive comps.
    Pin 12 should show the 19KHz osc.
    Refer to the datasheet http://www.datasheetspdf.com/pdf/610174/MatsushitaElectric/AN363N/1
    Socket the AN363 part and try a new one.
     

Share This Page