SX-3700 Recap/Restore Thread

Discussion in 'Pioneer Audio' started by ohgoshjosh, Mar 11, 2018.

  1. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    No differences.
    Take your time, double check your work.
    Perform a good visual check while working the board.
     

     

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  2. MBuras

    MBuras Restoration is an Addiction Subscriber

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    I’m guessing someone just forgot to type the A. There is a difference with the CYTA vs YTA. The C suffix indicates center collector pinout ECB. Without the C suffix indicates a center base pinout EBC. I’ve seen a few people tripped up by the pinout difference.
     
  3. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    You want the ECB configuration. The other letters indicate the gain and the package type
     
  4. ohgoshjosh

    ohgoshjosh New Member

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    Finally got around to replacing the transistors and caps in the speaker protection circuit. The issue still isn’t fixed, but it seems like we’re making progress. Some observations:

    Prior to replacing the caps/transistors, on the DBT, the relay wasn’t making any noise at all. Now, after replacing them, on the DBT the relay is ‘buzzing.’ I take this as a promising sign, since power is now getting to the relay. Here are the power readings:

    Between the pins:
    TP48-49 (L ch): 15.5 mV
    TP47-46 (R ch): 2.1mV

    Test pins to chassis:
    TP48: 1.5mV
    TP49: -14.0mV
    TP47: 41.7mV
    TP48: 44.8mV

    Some of these readings are different than the first ones I took. TP48 is now only 1.5mV, and TP49 is completely different. Any ideas where to go from here? I’m afraid to take it off the DBT.
     
  5. quaddriver

    quaddriver 120 What's per channel Subscriber

    what do you mean its buzzing? its a dc coil...is it cycling in and out hyper fast such that it buzzes?
     
  6. ohgoshjosh

    ohgoshjosh New Member

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    So, I had almost given up on this guy. I was ready to pack it all up, when I plugged it back into AC (off the DBT). Sure enough, the relay clicked right on, and I'm getting output to the speakers! Looks like replacing the SPC did the trick. Now there's just one pesky little issue: neither of the flouroscan displays light up: neither the wattmeter nor the tuner. Where should I start with these?
     

     

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  7. ohgoshjosh

    ohgoshjosh New Member

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    Bumping -- Back into this project. With the protection issue solved, I'd like to see if I can't get the FL Power Meter and FL Tuner displays working again. I'm hoping the IC's aren't damaged, and wondering if there is a power issue. Before I go swapping out the caps and transistors in the Power Amp, I wanted to see if I could get another eye on these readings, and if you could point me in the right direction toward figuring out where the issue lies in for the FL displays. How can I test the IC's?

    (Readings on the DBT)

    Pin: Reading
    20: 28.2V
    22: 6.8V
    25: -21.9V
    26: -12.9
    23: 13.3V
    24: No pin

    18: No pin
    19: 0V (0V)
    21: 0V (0V)
    27: No pin

    30: 26.8V (25.9V)
    31: 26.8V (26.0V)
    29: 26.3V (26.1V)
    32: 0V
     
  8. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    How about the board readings from AWV-012?
    Pins 7 and 8 are AC.
    Pin 4 -27v DC?
    C1 and C2. What caps are installed? Tantalum's?
     
  9. ohgoshjosh

    ohgoshjosh New Member

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    Pins 7-8: 0.6 VAC
    Pin 4: -27 VDC
    C1 and C2 look like standard electrolytic caps to me :dunno:
     
  10. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Pins 7 and 8 should have voltage.
    I can’t remember. 7 volts +-?
    It’s in the full system scat. I’m at work. No access to data.
     
  11. ohgoshjosh

    ohgoshjosh New Member

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    Should be 7.5VAC according to schematic. Each pin running about 3VAC
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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    ohgoshjosh likes this.
  13. ohgoshjosh

    ohgoshjosh New Member

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    Thanks, seems you were right. Those transistors in the SPC work just fine now, so I’m guessing it was either an error in the repair manual or perhaps Pioneer had some nominally different spec? Anyway, all good on that front for now.
     
  14. LesE

    LesE 110284 Subscriber

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    The suffix can sometimes indicate that the selected device has improved specifications.

    (The following is from the Tuning Fork docs)
    Pioneer TF-3.jpg

    Pioneer TF-1.jpg

    Pioneer TF-2.jpg
     
  15. ohgoshjosh

    ohgoshjosh New Member

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    Thanks for that excerpt from Tuning Fork. There doesn’t seem to be an immediate need to replace the one I just swapped out at the moment, but good to know for the future. This thread seems to have some insight on what that 2SC945A would be: http://audiokarma.org/forums/index.php?threads/i-cant-find-a-2sc945a-what-to-do.149389/

    Bookmarking for future use.

     
  16. onwardjames

    onwardjames Hoardimus Maximus Subscriber

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    watching with great interest
     
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  17. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    Fuse F4?
     
  18. ohgoshjosh

    ohgoshjosh New Member

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    Oh yeah, that one looks like it’s a gone-er. Gray/brown in the middle. Reading >9 Ohms on the Circuit Board since I didn’t want to mess with removing it. I had already cleaned up the PCB, but I guess I didn’t notice with all the dusty wires nearby it. I’ll replace that one and see what happens.
     
  19. GTS Dean

    GTS Dean New Member

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    Thread referenced!
     
  20. ohgoshjosh

    ohgoshjosh New Member

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    Well, it took me a minute to get a fuse puller. I’ve now got power back to the Flouroscan displays. When I powered on (on the DBT still), the relay engaged and I was initially getting power to the outputs. It looked like I was reading a DC offset, and I was (Right channel fluctuating wildly between 20-70 mV). When I powered off the unit and powered it back on, I’m now back without power to the outputs. The relay doesn’t engage, and is making a ‘buzzing’ sound. Something is still going on here, and I’m wondering if the issue with the right channel is part of it. Too much DC going to that right channel perhaps?

    So, for a brief moment it looked like we had addressed the major issues, but now it seems like there is still something wrong here. Any ideas where to start looking?
     

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