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Kenwood CS-4035 Oscilloscope repair questions

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    #21
    Re: Kenwood CS-4035 Oscilloscope repair questions

    Originally posted by stj View Post

    btw, TO 072 is probably supposed to be TL072
    Yeah, clocked that when I went to look it up.

    At least it is common enough to replace.

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      #22
      Re: Kenwood CS-4035 Oscilloscope repair questions

      So, when going to measure across the cap it became apparent that there was abreak in the trace where the cap had been. Fortunately it was on the Gnd pin side which makes reconenction easier.

      It'll have to wait a few hours now though as the day has arrived.

      I'll also take some readings at the pin holes with the IC removed and then we can compare how much the hybrid is affecting things.

      Back later

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        #23
        Re: Kenwood CS-4035 Oscilloscope repair questions

        Apologies for the delayed response but had an accident and lost a day.

        Originally posted by redwire View Post
        Can you measure voltage across the new cap,
        It reads -4.9v

        Testing the zener with a component tester comes back as 5.2v


        What really doesn't make much sense is pin 11 (-8V feedback pot) reads more negative when pin 10 is more positive.
        Double checked the voltages just now and that is what they are...


        I suppose the next step must be to replace the op-amp?

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          #24
          Re: Kenwood CS-4035 Oscilloscope repair questions

          Originally posted by redwire View Post

          What really doesn't make much sense is pin 11 (-8V feedback pot) reads more negative when pin 10 is more positive. That's either a bad measurement or that op-amp has a failed input.
          Just realised that by adjusting the VR1, that pin 11 can go from -0.3, down to -5.00v

          Pin 10 is still on -9.5v

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            #25
            Re: Kenwood CS-4035 Oscilloscope repair questions

            Quick progress report on the Kenwood KMA 01 Hybrid IC repair

            Replaced the TL 072 Op-Amp and now have variation on the -8 voltage.

            It currently swings from -9.50 at one extreme, down to -8.86 around the middle region, and back up to -9.50v at the other extremity.

            I am hoping that the voltage is high due to no load on the output, however, we do seem to be getting somewhere with this hybrid IC.

            The voltage across the capacitor is now 5.03v (the zener is 5.1)

            Gonna now move on to the main board and see if whatever is bringing the rails down can't be located and resolved.

            Wish me luck!

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              #26
              Re: Kenwood CS-4035 Oscilloscope repair questions

              Excellent news to report...

              These Kenwood Cs 40xx series are repairable.

              The scope is fixed and working!!!

              The reference voltage is now adjusting properly, so just need to calibrate it.


              Thanks for the help and suggestions.


              Now I have to get the second one done, and I think it only right to document and photograph the repair process of the KMA01 on that unit and post it on BadCaps for future reference.
              Last edited by Crystaleyes; 05-08-2022, 04:23 PM.

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                #27
                Re: Kenwood CS-4035 Oscilloscope repair questions

                Hey that's great news
                I could only see a few voltage readings implying the IC was bad.

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                  #28
                  Re: Kenwood CS-4035 Oscilloscope repair questions

                  Originally posted by redwire View Post
                  Hey that's great news
                  I could only see a few voltage readings implying the IC was bad.
                  Hi fella.

                  Yeah, I'm chuffed.

                  On other threads people had given up on finding the IC's. The general vibe seemed to be to scrap the Kenwood scopes, but it was straightforward on this one, even if I still don't understand exactly how it all works.

                  These two scopes here have had considerable repairs and tweaks and the short on the main board turned out to be where whoever had changed an electrolytic, had bent a leg (to hold it for soldering) and had almost invisibly shorted that to Gnd.

                  All good now, just calibration and some noisy switches to resolve.

                  Big respect and thanks to you and stj. You have literally saved two scopes from the scrapyard

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                    #29
                    Re: Kenwood CS-4035 Oscilloscope repair questions

                    i knew the hybrids would be bad.

                    in the arcade business Konami uses ceramic hybrids with smd electrolytics on them - and they ALL fail!!

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