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Balance control problem on Panasonic SG-999

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  • Balance control problem on Panasonic SG-999

    Have a vintage Panasonic SG-999 integrated stereo, pop up turntable experiencing a strange balance control problem. On one channel, the balance control works fine, meaning if you start center and go to one end it attenuates and fades the signal on that channel down to zero. On the other channel, the control has no effect. It is always on, regardless of the balance control setting. I disassembled and removed the balance pot (R4 on the schematic, 100K with three terminals). Was certain that had to be the problem but using a resistance meter, center pin to end pin(s), it seems to work fine. Reads about 61K to zero as you sweep the control, on both pin combinations. So if the pot is good, there must be something in the circuit bypassing the signal through, ala short someplace, but only in the one direction. Where in the signal path should I be looking? Link to a portion of the schematic is here:
    http://home.comcast.net/~jimkarl/Pan...schematic1.jpg

    Both channels sound fine and equal volume-wise but this balance control circuit isn't working properly.

  • #2
    If you read 61K across a 100K pot it's probably bad. What do you measure across the 2 outside terminals of the pot? Try shorting out the center terminal to each of the outside terminals in turn. That channel should go quiet. Or reverse the 87 & 104 wires on the pot and see if the problem switches sides. Interesting circuitry; all returns to 6.4 volts instead of ground.

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    • #3
      Originally posted by adnadeau View Post
      If you read 61K across a 100K pot it's probably bad. What do you measure across the 2 outside terminals of the pot? Try shorting out the center terminal to each of the outside terminals in turn. That channel should go quiet. Or reverse the 87 & 104 wires on the pot and see if the problem switches sides. Interesting circuitry; all returns to 6.4 volts instead of ground.
      I thought 61K was low too, but I figured it was 61K per side, 120K across so that was within 20% tolerance.
      Problem turned out to be a broken trace on the circuit board. One of the pots leads that came back to the board made it ok, but the trace was broken along the way to the the other components. Looked like corrosion had eaten through. I had to jumper over that spot,. All works perfect now.

      Was strange that 6.4 V came into center (was actually measuring about 4.8) but anyway first time I've seen a circuit design like like. In any case - all is working fine now.

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