Tuner: No sound except for Multipath

Discussion in 'Tuners' started by dbxdx5, Apr 24, 2017.

  1. dbxdx5

    dbxdx5 AK Subscriber Subscriber

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    I'm a relative noob when it comes to fixing tuners and could use some troubleshooting direction. The tuner in question is a Mitsubishi M-F01. When I have it hooked up to a preamp and tune in a station (based on the signal strength meter and lit up "lock" light), there's no sound from either the Fixed or Variable outputs I have to choose from. But if I switch to the FM Multipath outputs, I get music.

    2017-04-24 21.02.37.jpg

    Of course, it may be just a matter of me studying the schematic and looking for leaky capacitors and bad solder joints.
     
  2. Punker X

    Punker X AK Subscriber Subscriber

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    Could be muting and or alignment. You are hearing the detector out. This is before the MPX section. If you get a locked stereo light, the MPX is probably ok and your problem would be in the ouput amp/buffer or muting circuit.
     
  3. dbxdx5

    dbxdx5 AK Subscriber Subscriber

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    This helps. Thanks.
     
  4. dbxdx5

    dbxdx5 AK Subscriber Subscriber

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    One other thought: Could the symptom described also be due to dirty tuner gangs?
     
  5. Punker X

    Punker X AK Subscriber Subscriber

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    Doubtful.. Doesn't hurt to clean, and may help with operation once you get audio, but not your issue here.
     
  6. dbxdx5

    dbxdx5 AK Subscriber Subscriber

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    Yep, I was grasping there...

    Found a few bad caps and decided to replace most of the electrolytics while I'm at it. I'll let you know how it goes.
     
  7. ovaeasy

    ovaeasy The Fifth Resident Subscriber

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    I sort of have the same issue with a Kenwood KA-9900. All three meters seem to show that I have a signal that is tuned, stereo light is on, and deviation meter is bouncing, but no sound. I found a blown fuse on the power supply board, replaced it since it had a rough ride in shipping, but blew again.

    That's as far as I've gone for the moment as I am moving this week. Might be a while before I can get back to it. Good Luck.
     
  8. blhagstrom

    blhagstrom Mad Scientist, fixer. Subscriber

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    Blown fuse the blew again = repair time.

    Moving closer to me?
     
  9. ovaeasy

    ovaeasy The Fifth Resident Subscriber

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    Sorry, but no. Prefer to stay south of the Pierce/Thurston County line. Tuner is on the shelf for a while as I'm deep into a SUMO Polaris with one dead channel.
     
  10. dbxdx5

    dbxdx5 AK Subscriber Subscriber

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    OP again: In the process of replacing many of the electrolytics in this M-F01, I've found that in one spot either the schematic is wrong or the wrong cap had been installed at some point. According to the schematic, both C309 and C310 should be 4.7uF 25V, however, when I removed them only one was 4.7uF and the other was 47uF. Unfortunately, I didn't pay attention to whether the 47uF was in C309 or C310. So now I'm left wondering whether the schematic is correct and both should be 4.7uF or if there's a typo and one should, in fact, be 47uF (and if so, which one).

    https://drive.google.com/file/d/0Bwa4OfIAUevwcC1sSWVBeTFQeFk/view?usp=drivesdk
     
  11. Punker X

    Punker X AK Subscriber Subscriber

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    I would put money on C310 being the 47uF. If they look original I doubt somebody changed them. Scats and manual are often are wrong. Or design changes are made during the run and they are not updated.
     
  12. dbxdx5

    dbxdx5 AK Subscriber Subscriber

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    I went with the 47uF for C310 and finished the rest of the recap. I'm now getting sound in Fixed and Variable. Thanks for the guidance.
     

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