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Carvin X-60 channel switching issue.

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  • Carvin X-60 channel switching issue.

    I have a Carvin X-60 with a low clean channel volume and very distorted( not the good kind), clipping drive channel. All tubes are good, all voltages present including low voltage to IC's. Have subbed all 4558 IC's with no improvement. I just noticed that when switching channels both leds light up on the face plate. I have the correct footswitch and it is behaving as it should but the front panel indicators are both lighting when in drive channel and neither lights when in clean mode. Any help appreciated!
    Carvin x30-x60.pdf

  • #2
    Check that the channel switching logic provides proper signals to drive the channel switching FETs: One control signal should be "high" while the other is "low" and vice versa. Check the condition of the inverter chip IC5, (4049 I presume), which practically is the switching logic. Each inverter within the chip should convert "high" input to "low" output or vice versa. Check the condition of the four channel switching FETs working in series/shunt pairs.
    Last edited by teemuk; 10-02-2014, 10:19 PM.

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    • #3
      Hmmm, I have the older version which does not specify the logic chip part number on the schematic. The newer schematic shows 4049 but my amp has a NTE4050B.

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      • #4
        4050 is a hex non inverting buffer, it has the same pin out as a 4049, so put a 4049 in there & see if that fixes it.

        Another version of the sch attached
        Attached Files

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        • #5
          It appears as if someone replaced the inverting buffer ic (CD4049) with the non inverting ic (CD4050).
          For sure it did not come from the factory with an NTE ic.

          Anyway, it still does not make sense that the Lead channel would turn on both LEDs.
          Looking at the schematic, if Lead drive is off (switch not connected) then IC5 pin 14 is at a Hi (because it is connected to +15V through R28 (680 ohms).
          Being the wrong buffer (non inverting) a Hi on pin 14 will drive pin 15 Hi. That will drive pin 3 Hi & pin 9 Hi.
          Pin 3 is the buffer input for the Lead LED. If 3 & 9 are Hi it will send the rest of the buffers Hi & illuminate Both LEDs.
          The Clean channel should be turning on both LEDs.

          So what you posted is either incorrect or the ic is really blown.

          At any rate you need to find the correct CD4049 IC.

          Note: the CD4049, being an inverter, will output the opposite logic state of the input.
          A Hi in becomes a Lo out.

          The CD4050 is a non inverter. The output will be the same logic level as the input.
          A Hi in becomes a Hi out.

          If you follow that Hi becomes a LO logic, the schematic makes sense.
          You will see that with the Lead switch off, pin 14 is Hi & pin 15 will be driven Lo.(and so on down the line)

          EDIT: Moz posted a different schematic. The ic pin numbers are different.
          I used the one posted by the OP for this explanation.
          Attached Files
          Last edited by Jazz P Bass; 10-03-2014, 12:23 AM.

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          • #6
            I'll ha ve to order a 4049.

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            • #7
              Here is a list of the Major parts houses that carry the ic.
              CD4049UBE Stock and Price by Distributor | FindChips.com

              You want to order the CD4049UBE.
              (Latest & greatest, lead free compliant, blah, blah, blah.)

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              • #8
                I installed the proper CD4049 chip and replaced R132 with the correct value. I then repaired the previous repair to the footswitch cable. Amp working great now, just need a new reverb tank. Thanks for your assistance, gentlemen!

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