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ROLAND DAC-15D only dry signal

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    #21
    Re: ROLAND DAC-15D only dry signal

    Hi, I made a first measurement, sinusoidal input signal of 1khz at 500mv with signal generator, tested with the oscilloscope at point 1 waveform, and I don't see anything at all, instead I should see a square waveform at 6, 5Vpp. I've posted the service manual page, I think I've set everything correctly, I think because I'm not 100% sure
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      #22
      Re: ROLAND DAC-15D only dry signal

      Hi everyone, I took a step back, and before delving into the world of signals over time, I started again to measure the voltages arriving at the circuit immediately after the transformer and rectifier bridge, and I noticed a voltage at the ends of Q2 which doesn't add up to me, it should be +7v and instead it gives me more than double, instead at the ends of Q1 it is correct -7v, I measured carefully several times so I'm sure of it, it could be the capacitors or some component, or it could actually be Q2 the problem? I attach the photo of the circuit and the measurements I made, Greetings Mauro
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        #23
        Re: ROLAND DAC-15D only dry signal

        Doesn't look right. Check the voltages at both the zeners going into q1 and q2.

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          #24
          Re: ROLAND DAC-15D only dry signal

          q2 appears shorted or d3 is open or has bad connection . it should measure 7.6v

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            #25
            Re: ROLAND DAC-15D only dry signal

            I checked the voltage at the ends of the zener diode, and indeed there was a broken solder, now the -7v and +7v voltages are correct, but the effects are still not felt. Excluding and hoping that ic7 controller is ok, I start to think that it could be a bad electrolytic capacitor, or some transistor. I'll gradually start checking the ESR of the caps etc, and then I'll move on. even with the oscilloscope, for now I don't think I can do anything else, thanks and greetings to all of you enthusiasts.
            Mauro

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              #26
              Re: ROLAND DAC-15D only dry signal

              Originally posted by Mabot17 View Post
              Hi, I made a first measurement, sinusoidal input signal of 1khz at 500mv with signal generator, tested with the oscilloscope at point 1 waveform, and I don't see anything at all, instead I should see a square waveform at 6, 5Vpp. I've posted the service manual page, I think I've set everything correctly, I think because I'm not 100% sure
              You need to follow the input waveform around giong by the points that you have posted from the service manual. You previously posted waveforms from point "2" (I think). So you need to do the same for each point as identified by the pictures in the manual. The one of interest is at point 3.

              Having said that, IF the voltage output was at 15v as you posted, it is possible that it might have taken out a few components that rely on the 7.x volts.

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                #27
                Hi everyone, it's been a while, I hope you're still with me. I finally repaired the amplifier, after various tests only the main controller remained as a suspect. I was lucky and found a working one. To make a nice work, I placed a socket and cleaned the PCB. Now everything works, I gained a lot of experience and I also had fun in the wasted time. I greet you and put a photo of the final work, good work everyone, bye. MauroClick image for larger version

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