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Pioneer SX-3700 Display Going Dark

Discussion in 'Pioneer Audio' started by jnunzir, Oct 28, 2018.

  1. jnunzir

    jnunzir New Member

    Messages:
    6
    I have a 3700 that just started having display problems. After it’s on for for a bit, the level meter, display lights and the am/fm display all go dark. I still am able to get sound from when I try all the inputs. If I turn it off and let it sit a few minutes, everything is turns on as it should. Then after a while again I lose all the lights and displays. Anyone ever seen this happen before? Hoping someone might know where I should look first.
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    Is it just the flouriscan that fades out? Did a little searching. Not very promising. VFD is dying.
     
    Last edited: Oct 28, 2018
    jnunzir likes this.
  3. jnunzir

    jnunzir New Member

    Messages:
    6
    I lose the two fluroscan displays and the lights that light up the tuning scale. I still have the lights on the selector buttons (ie: speaker a & b, fm, am, aux, phono) those still function and light when the fluroscans and the tuning scale lights go out.

    And they aren't fading out, they just go out/off. As I mentioned before, if I turn it off for a bit, they'll come back on. If I try turning it off and on and off and on, etc. right after they go out, they don't come back on. It has to sit for a few minutes
     
  4. cnyel1967

    cnyel1967 AK Subscriber Subscriber

    Messages:
    1,015
    Location:
    Ohio
    From what I have heard and read, this series of Pioneer were prone to loose or bad solder joints on the large or long board. I had a SX3900 that had that happen to but if I moved it around or tapped the sides, many times the display and sound would come back on.
     
    jnunzir likes this.
  5. markthefixer

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

    Messages:
    21,088
    Location:
    Bensenville,Illinois
    It's a power distribution wiring problem (cracked slobber joint?) or the FU4 3 amp fuse has gotten tired.

    INDEPENDENT lighting areas to stringently VIEW and report:

    am / fm / phono / aux 13v DC through 150 ohm dropping resistor to one of four 8v 50mA lamps
    speaker a / speaker B 7.5vac to 8v 50mA lamps (no dropping resistor)
    main panel lights 7.5vac to three 8v 300mA wedge lamps. (no dropping resistor)
    VU display 7.5vac through 2 x 18ohm dropping resistors for heater
    Tuner display. 7.5vac through 2 x 12ohm dropping resistors for heater


    Power Supply, 7.5vac from the transformer. FU4 3 amps on the power amp board and the pads NEXT to it that have a jumper wire are the inlet and distribution point for the main panel lights, the two fluorescent display modules (their heaters with appropriate dropping resistors: 2x18 ohms for VU and 2x12 ohms for tuner) and the speaker indicators (the am, fm, aux and phono run on 13v dc through a 150 ohm dropping resistor).
    It comes from the blue transformer wires connected to pins 7 & 8.
    It goes through the fuse and the jumper where the pads for another fuse are.

    so:

    Check fuse for fatigue and sagging,
    Check solder joints or just (if you are good at soldering) resolder them.

    The time delay to lights out / back on is a heating / cooling cycle that has invaded some solid wiring. The additional resistance of the defect causes heating expansion and eventual disconnection, then it cools and reconnects itself as it contracts.

    I may, if we have trouble, go back and edit THIS post to explicitly call out each pin that carries current to each of the named displays to locate the EXACT section of foil on the pc board.
    I HOPE it doesn't come to that.
     
    jnunzir, merlynski and redk9258 like this.
  6. jnunzir

    jnunzir New Member

    Messages:
    6
    Thank you for all your replies! I'm going to look into everything you mentioned. I also have a SX-D5000 that is doing the same thing. I'll change all of the fuses regardless of how they look.
     

     

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  7. jnunzir

    jnunzir New Member

    Messages:
    6
    So I was able to work on the 3700 this weekend and started exactly where you said I should look first. I removed the top and bottom panels so I could have access the main board with fuse FU4. I notice that if I flexed the board slightly up and down that I could make the display flash on and off. I wasn’t able to see any bad solder joints from what I could tell but there were a few that definitely looked like they may have been cold joints. I decided to resolder most of the joints near FU4, including the fuse holder itself. After completing the resoldering of at least 30 +/- joints, the problem seems to be fixed. When I tried flexing the board again, I was not able to duplicate display going on and off, as I did before the resolder. Apparently, one of the joints was the culprit. Whether it was the fuse holder joints or one of the circuits on the board, I do not know. I have ran the receiver extensively since the repair without losing any of the displays or illumination. For safety sake, I did purchase an ACInfinity receiver cooling fan that will help to keep the unit cool during operation. If you’re not aware of this product, I encourage you to check them out doing a search of that name on google or Amazon, which is where I purchased mine from.
    I want to thank you again for all of your help, helping me to diagnose the problem. I can only hope that if there is someone else out there with any of the SX models having the same problem, that this thread will be of some use to them. The Audiokarma members are a great asset to vintage audio collectors/enthusiasts and all of the knowledge is second to none!

    Thank you!
     
    Bruno Primas, cnyel1967 and redk9258 like this.
  8. markthefixer

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

    Messages:
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    Location:
    Bensenville,Illinois
  9. markthefixer

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

    Messages:
    21,088
    Location:
    Bensenville,Illinois
    I worked with a LOT of fan cooling in equipment. That NEEDED it. 3 fans full on pressurizing a chassis rack, 3 fans evacuating that same chassis rack. When one of the fans SLOWED, the error rate in the equipment as determined by QC records increased noticeably. A LOT of heat. Things HAVE improved, just a bit, since then.

    These chassis were on a 3 month PM cycle, and the amount of dust packed in there in a rather CLEAN (but NOT cleanROOM, we had those too!!) environment soured me on the idea of fan cooling. The insides of fan cooled tower and laptop PC's have never been able to change my opinion of fast moving air's troublesome nature as a dust magnet and dust trap. Trapped dust insulates badly, and conducts too.

    As you can tell I am not a fan of fans...

    Guidelines:
    SLOW air movement
    LOTS of room for the heated air to move upwards
    no restrictions, plenty of space between fins
    adaptive cleaning schedules - find a lot of dust you go back in SOONER!!
    You need to get the air IN first
    then you need LARGER exits for the hot air.
    when the air is slow, and unrestricted, the dust can drift out just as it drifts in.
     

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