Technics ST-8044 No Output

Discussion in 'Tuners' started by xs650shawn, Apr 16, 2017.

  1. xs650shawn

    xs650shawn Active Member

    Messages:
    170
    Picked up a Technics ST-8044 from the swap meet yesterday. Fairly clean cosmetically, inside is spotless. Looks like it has never been opened. Passed the dim bulb tester. Hooked it up to my JVC integrated, and got no sound. Just to verify, also hooked it up to my Technics receiver, in both the Aux and Tape In connections. Still no sound, but what is even more odd, it is tripping my speaker protection circuit. Didn't do this on the JVC, just the Technics.
    Already looked at the "service manual" on Hi Fi Engine, really only shows how to do alignment and not much else. So question is, where to possibly look for a cause of lack of sound, but also why would it trip my protection circuit? IMAG0840.jpg IMAG0841.jpg IMAG0840.jpg IMAG0841.jpg
     
  2. sregor

    sregor AK Subscriber Subscriber

    Messages:
    3,071
    Location:
    Mass
    A couple questions. Any indications? signal strength, stereo light, meter deflection as tuned? Also, as far as the protect - try one input at a time into the amp. Does it cut out on both aux and tuner? Also check bottom of PC board for cracks, especially around mounting screws. Do you have access to scope or someone with a scope. If you can't see anything, first check would be power supply, then voltages on IC's. Good luck with it.

    Aside - I call these "upside down tuners" with all the controls on the top and the dial on the bottom. I've seen a few others but can't recall which models and makes....
     
  3. xs650shawn

    xs650shawn Active Member

    Messages:
    170
    Will read as tuned when dialed to known stations, all lights, including "servo lock" work. Was only using one input at a time, protection circuit trips with either, but only when connected to my receiver, not when connected to my integrated. Unsure how "sensitive" the protection is on my integrated, but I know it seems to be working. To elaborate, it trips the protection when on and connected, if I try turning the volume up. There continues to be no sound, no matter how much I turn it up. Protection kicks in at less than 1/4 volume. Bear in mind, no other input has ever caused this, so I am certain it is not my receiver, but something with this tuner. No access to a scope, but do have a multi-meter.
     
  4. Punker X

    Punker X AK Subscriber Subscriber

    Messages:
    3,880
    Location:
    Panic in Detroit
    Only thing I could think is that there is DC voltage on the output. There are output coupling cap that should prevent dc from affecting what you attach it to. You may want to look at your amp. Your DC offset may be off a bit.

    If everything seems to work then, not much. Looking at the scat, my guess would be a muting issue. This tuner uses a couple of transistors to short the ouput, plus a few others to trigger the muting action.

    Manual available at hifiengine.
     
  5. xs650shawn

    xs650shawn Active Member

    Messages:
    170
    Based on the manual, output voltage should be 0.6v. I'm measuring 9.4v DC at the outputs. Ideas? I've only got $10 into the thing, if I take it to my repair shop, it's $30 just to start. Is this tuner even worth that?
     
  6. sregor

    sregor AK Subscriber Subscriber

    Messages:
    3,071
    Location:
    Mass
    Dc should be 0 volts DC. The .6 volts is AC and refers to the audio signal. I'm wondering if someone tried to by pass the muting circuit. There should be DC on wires coming from pins 100 and 101, but no DC on the ones coming back on pins 102 and 103. If there is a muting issue, I would start by disconnecting (unsoldering) collectors of .q451 and q4452 (disables muting entirely, so get ready for noise) There are two caps in series on the muting board, I can't believe both (or even one) are shorted. YMMV
     
    Last edited: May 11, 2017

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