SX-950 Project

Discussion in 'Pioneer Audio' started by Motnick, Feb 6, 2018.

  1. petehall347

    petehall347 the brandy coffee man Subscriber

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    output of fm might be low ..coupling cap issue maybe. or bad switch contact .
     

     

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  2. petehall347

    petehall347 the brandy coffee man Subscriber

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    or other issue with fm circuit ..is it all channels across the dial ?
     
  3. Motnick

    Motnick AK Subscriber Subscriber

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    Yes. The issue is there on any and all FM stations.
     
  4. Motnick

    Motnick AK Subscriber Subscriber

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    Looking at the schematic some more, it looks like the FM function switch is about the only thing it could be outside of the tuner board.

    I think I’ll try to measure the resistance across that switch to see if one side is different than the other. Maybe it just needs more cleaning?

    Is it possible to measure the signal coming out of the tuner board left vs right to see if one channel is weaker?
     
  5. markthefixer

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

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    Yes, use an improvised signal probe from an interconnect cable and a coupling capacitor (0.1uf is fine, connect it to the center lead, probe with the other cap lead) plugged into a tape monitor input.
    Then you will depress the tape monitor switch to cut it in (don't be surprised that the OTHER channel is quiet - this is using ONE channel like a scope for your ears) and probe the tuner points looking for the difference in volume levels.
    Turning to the AWE-066 tuner board - there are several points where the signal level of one channel can be impaired.
    here's a list, in signal flow order:
    Q8 HA1196 chip pin 4 (L) and 5 (R) source
    AWE-066 pin 16 (L) and pin 14(R) wiring before filter or coupling caps
    Next is coupling caps C43(L) and C44(R) passing the signal to the Filter.
    AWE-066 F5 - this filter can die in one or both channels. If you get to that point, and want help, post a picture of the top of the tuner board (the bottom is inaccessible) for visible probe points.
    Then there is a muting circuit,
    Has C57 in the tuner's muting circuit been replaced - hopefully it ISN'T a sky blue Sanyo CSSA type crappy capsistor!! That has caused problems before. This is a LOW probability cure.
    The muting is Q10 and Q11 and they share the emitter(grounded) and base (muting control) connections.
    Unfortunately they are hard to test in circuit, because it is hard to tell if the signal is getting hurt in the F5 filter or by Q11 in the right channel.

    edit - something I forgot:
    FIRST- Ohming the switch contacts directly is difficult as the switch board is buried, on the AWS-094 board, input is pins 42(L), 40(R) and output is pins 45(L), 44(R).

    So take an ohms reading (with FM selected) from AWE-066 pin 11 (Left) to AWG-038 flat amp(rut roah!!) pin 12 to establish a baseline, then for the RIGHT channel AWE-066 pin 12 (Right) to AWG-038 flat amp pin 11.

    Then, if the ohms test is good, you need to make the signal probe, so probe here FIRST:
    AWE-066 pin 11 (L) and pin 12(R) - these are the outputs of the board, check them for equal levels FIRST.
     
    Last edited: Feb 13, 2018
  6. Motnick

    Motnick AK Subscriber Subscriber

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    Thank you mark. This is awesome!

    I think I’ll take a closer look at the fm function switch first to ensure that it is functioning properly, then I’ll work on making up the signal probe that you described.
     
  7. Motnick

    Motnick AK Subscriber Subscriber

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    Let’s start with the simplest thing first. Let me show you what I am working with here.

    [​IMG]

    C57 has not been replaced and it is indeed a sky blue Sanyo.

    Please correct me if I am wrong here, but it looks like C43 and C44 are both blue tantalum caps. It also looks like the same blue caps are installed in C37 and C38. The manual claims that all four of these should be electrolytic.
     
    Last edited: Feb 14, 2018
  8. Motnick

    Motnick AK Subscriber Subscriber

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    Both sides of the switch measure .5 ohms. My Craftsman meter reads .4 ohms with the leads shorted together. So it looks like the switch is not the issue here.
     
    Last edited: Feb 13, 2018
  9. markthefixer

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

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    Ok, the probing points from above (I won't point (pix) because you are slinging cap numbers around pretty well) in the stereo signal path from the stereo decoder chip Q8 HA1196 chip pin 4 (L) and 5 (R) source. to the output of the AWE-066 tuner board on pins 11(L) and 12(R).

    These probe points are the ends (both sides) of the named resistors.

    If the filter is loading it's input, R42 will have a severe signal drop from end to end.
    edit - whoops, r42 is 47k while r44 is 3.3k, so r42 will see the drop in signal NOT r44 at 3.3k.

    If the mute is loading the filter output R68 will have a severe signal drop from end to end.

    left
    Q8 HA1196 chip pin 4 (L)
    R41 47k yellow violet orange gold
    Can't hit C43, so we get the resistor on the other side
    R43 3.3k orange orange red gold
    Other side of this is the filter input
    Filter output
    R68 910 ohms white brown brown gold
    muting transistor Q10 and board output pin 11

    right
    Q8 HA1196 chip pin 5 (R)
    R42 47k yellow violet orange gold
    Can't hit C44, so we get the resistor on the other side
    R44 3.3k orange orange red gold
    Other side of this is the filter input
    Filter output
    R69 910 ohms white brown brown gold
    muting transistor Q11 and board output pin 12
     
    Last edited: Feb 17, 2018
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  10. Motnick

    Motnick AK Subscriber Subscriber

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    Thank you Mark. I have printed out the schematic and the PCB layout from the manual, and marked out all of these test points. It looks like this should not be a big deal once I have the signal tracer built.


    I will need to order a 0.1uf cap as I don't have anything that size on hand. What do you suggest I use for this?

    Should I add any tuner board parts to the order just in case?
     
  11. markthefixer

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

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    do you have ANY caps with lead length? 0.1uf is just a start.

    an electrolytic cap can be used, with the minus to the interconnect lead, if you have TWO electrolytic caps put them in series with the minuses connected and use one plus to the cable center lead and the other plus is your probe.

    tracer_probe.jpg
     
  12. Motnick

    Motnick AK Subscriber Subscriber

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    I dug a little deeper last night and found some parts that I had forgotten I had. I found this Panasonic film .1uf/250v with nice long leads. Will this work?

    [​IMG]

    I was also wondering, do I use the 950 or another receiver to plug the signal tracer into. I also have a Technics SA-200 that I could employ for this.
     
  13. markthefixer

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

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    The 950, the procedure was developed specifically to use whatever unit had the problem.

    That cap is fine.
     
  14. Motnick

    Motnick AK Subscriber Subscriber

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    I made up the signal tracer this morning. Wow that works amazingly well!

    Starting at pin 11 and pin 12 and working back through the circuit at all listed points, the volume is lower in the right channel until I cross R41 and R42. The volumes equal out on the Q8 side of those resistors. Volume is equal at Q8 pin 4 and pin 5.
     
    Last edited: Feb 17, 2018
  15. markthefixer

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

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    Ok, remove F5 and check that the volume comes up at the low points. WHEN it does, you obviously need a new F5, ATF-033.

    It can be donated from the SX-650, SX-750 (not the tuner board, the AWM-094 board), SX-850, SX-950.
    NOT the SX-1050 or SX-1250, they use the atf-028 and are very different.
    NOT the SX-x80 series, the pa1001 stereo decoder chip uses pilot nulling or an ATF-047 filter.

    edit - sent you a private message.
     
  16. Motnick

    Motnick AK Subscriber Subscriber

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    So that I know, (still learning here) how did you rule out the coupling cap C44? I would have suspected C44 since it’s in between R42 and F5.

    Not questioning you here, just trying to keep up with you and learn to understand the logic.
     
  17. Motnick

    Motnick AK Subscriber Subscriber

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    By the way, although the service manual lists F5 as ATF-033, the part on my tuner says ATF-042.

    [​IMG]
     

     

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  18. markthefixer

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

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    The level was the same on each side of the capacitor. The confirmation is the removal of the short (ed filter) and the levels equalize across the board (well until the missing filter interrupts the further progress of the signal through the board).
    Part of it is understanding how the cap fails, usually high impedance. But through 47k, it's hard to drop the signal that much. So the 47k resistor shows the signal difference across it when it's firing into a much lower impedance (cap, 3.3k, shorted filter.)


    ATF-042.... hmmm that one wasn't on the radar AT ALL!!
    More losses because Pioneer is pruning their old parts database.
     
    Last edited: Feb 17, 2018
  19. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Pull it off the board carefully. You might see the issue. Some corrosion, broken hair wires? You might salvage it?
     
  20. Motnick

    Motnick AK Subscriber Subscriber

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    I pulled out F5 and the same issue remains.

    Perhaps I wasn’t specific enough about what I am actually seeing. Let me try to give more details.

    Measuring at Pin 4 and 5 of Q8 the volume is equal. Measuring at the Q8 side of both R41 and R42 the volume is equal. When I cross over to the coupling cap side of both R41 and R42 the volume increase in both channels, but it increase more across R41.
     

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