CX-830

Discussion in 'Yamaha' started by nazrin, Apr 10, 2018.

  1. nazrin

    nazrin New Member

    Messages:
    20
    I have a preamp CX-830 which controls the MX-830

    I've had two amps connected to this preamp and have the sample problem

    the sound is completely turned off for about 4-6 sec then back on.....does it randomly, 4 times in an hour or better.....like something warms up then the sound goes off for this time then back on

    I am certain it is the preamp doing it......What should I look for or replace within the PCB to fix this problem?
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    Whats your geographical area ? The problem could be a number of things. Need a little more info. Does it matter what input is selected ? What inputs are you using ?. It could just be a cold solder connection. I'm assuming this occurs in both channels. Common circuit to both channels is the power supply.
     
  3. nazrin

    nazrin New Member

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    It cuts off sound completely, yes both channels, and it does not matter which input I select. I use the Rec out knob as I have an EQ and mainly us CD,tuner, LD

    The power stays on while both channels cut out....
    Oh, thanks for your reply, I’m in central maine
     
  4. avionic

    avionic " Black Knights " Subscriber

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    Part of the power supply is working if the LED's stay illuminated.Do you know how to follow and schematic diagram ?
     
  5. avionic

    avionic " Black Knights " Subscriber

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    Have a close look at Q72 and Q76 solder connections. These two are on the two large heatsinks.
     
  6. nazrin

    nazrin New Member

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    Yes, I can follow a schematic to some degree, where can I find a schematic to look for Q72 and Q76

    also, I can say no crackling during this on/off sound, very clean on/off.....wouldn't a bad solder connection have some noise associated with it?

    I'd love to figure this out, it's been doing it for 4 years now
     

     

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  7. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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  8. Mrv8q

    Mrv8q Well-Known Member

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    Have you eliminated the EQ as a possible culprit? Had an EQ in a system that exhibited similar symptoms, drove me crazy .

    A couple of cold solder joints in the EQ were touched up and solved the problem. Just a possibility...
     
  9. nazrin

    nazrin New Member

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    I will verify the EQ tonight
     
  10. nazrin

    nazrin New Member

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    I do know it is not the MX-830 as that is a new addition past few weeks
     
  11. nazrin

    nazrin New Member

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    So I turned off the EQ-630, with no EQ, after an hour it cut out three times in the next 45 mins....so it looks to be the CX-830
     

     

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  12. mbz

    mbz AK Subscriber Subscriber

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    The cs-830 has a mute circuit, maybe malfunctioning? Need to take a closer look.
    Is the off/mute period always about the same 4-6 seconds?
     
  13. mbz

    mbz AK Subscriber Subscriber

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    Probably a power supply problem to one of the opamps which is shared between L&R channels.
    Will try and get some test points.
     
  14. avionic

    avionic " Black Knights " Subscriber

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    This is going to be a bitch if it only acts up for a few seconds.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    If its a transistor intermittently failing.. Its going to be pretty rough nailing down the " root cause"...
     
  16. mbz

    mbz AK Subscriber Subscriber

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    The opamps of interest are fed by Q72 & Q76. Have you checked the solder connections as per above. Google dry solder joints for pic's
     

     

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  17. mbz

    mbz AK Subscriber Subscriber

    Messages:
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    Probable scenarios are,
    - power supply intermittent failure due to bad solder joint or transistor
    - intermittent opamp failure, much less likely.

    Two basic techniques,
    - monitor psu voltage
    - monitor audio signal with probe to find out where it fails

    The screen print from the service manual is not great.
    Need to identify the +18 and -18Vdc voltage rails that feed the opamps.

    With amp powered up normal, measure the dc voltage at jumpers J172,3,4 and J150
    as per pic. I'm guessing that 2 of these will be +/-18Vdc (approx). Need to put
    clips and set up 2 multimeters to monitor voltage.

    The audio probe is slightly easier but less likely to find the fault.

    The easiest solution is to check Q72, Q76 solder joints

    agree

    CX830.JPG
     
  18. nazrin

    nazrin New Member

    Messages:
    20
    Wow, thanks for this input and help. I have not opened the unit yet and yes, about 4-6 seconds.....

    I was considering the mute circuit as it sounds that smooth, on/off sound

    I was thinking the IR input was receiving a false signal or maybe the circuit was sending this signal internally
     

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