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GK 1001RB 2 - Problem passing self check

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  • GK 1001RB 2 - Problem passing self check

    Hello to everyone here on the forum. Long time lurker, first time poster. My condolences to everyone for the sad loss of Enzo.

    I have a GK 1001RB-2 on the bench I am trying to get running. First point to make is that this main power PCB shows 206-0260-A7 and I cant seem to find any schematic or doc showing the difference from A6. The previous owner stated they saw smoke. I am not able to find any physically damaged components besides the looks of R70 and R71 getting hot enough to make heat marks on the PCB and cause solder to deteriorate a little. Both R70 and R71 test out in spec out of circuit. Resoldered a few joints that looked suspicious from the ever-known issue of non lead solder usage. Resoldered all jacks. Checked majority of the diodes and resistors. Under heatsink, resistors and transistors that were able to be tested in circuit passed. Rectifiers seem to pass. Startup with Variac and limiter. Initial start up the fan wants to turn a few clicks and stops. At 120v I get Red power light and no change to Blue (or Green for that matter on some versions). During power on, there is no voltage at the bias test points. No DC offset on speaker outputs without load. After power off and another component sweep through, I find that C22 (600v mica 560pF) is reading 880pF out of circuit. Could this be causing some issues? I will have to order some of these as I do not have in stock. I'm not at my notes right at the moment but there were also a few diodes that did not have voltage was expecting (0v).

  • #2
    Before worrying about the cap, I'd first check that all of your power rails are there.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

    Comment


    • #3
      Hi Dude! A fair question. I got excited finally finding an out of spec component. It seems all the rails are ok at 120v main and off limiter, the +101 is showing +101v at the base of D17 and 0v at the top of D16
      Last edited by nickbme07; 08-30-2022, 06:09 AM. Reason: typo on rail voltage

      Comment


      • #4
        BR3
        +100v
        +72v
        +72v
        +43.5v

        BR1
        -100v
        -72v
        -20v and drops quick
        -43.3v

        BR2
        43v
        0v (32v AC)
        0v (32v AC)
        -43v

        Comment


        • #5
          I don't have an A7 schematic. All I have is this one (A6 towards the bottom). Is it at least close enough to work with and are designation numbers the same or similar? If not, it might be tough and confusing to offer help.

          gallien-krueger_1001rb-2_sch_[ET].pdf
          "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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          • #6
            Yes, I have been going by A6. The B schematic I think is different.

            Comment


            • #7
              How 'bout the +&- 15V supplies coming off of U4 & U5?
              Last edited by The Dude; 08-30-2022, 03:17 AM.
              "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

              Comment


              • #8
                I just checked the DC output offset and found a -0.38vDC on the left speaker jack tip to ground. Seems to show up when using 120v main and no limiter.

                I assume maybe the U6 is under the heatsink? I dont see on schematic.

                U5 shows +43.6v from PIN3, +15.4v on PIN2, +14.8v from PIN1
                Or did you mean U4: -15.4v on PIN3, -43.4v on PIN2, 14.1 on PIN1
                Last edited by nickbme07; 08-30-2022, 03:13 AM.

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                • #9
                  Yes. U4&5. My bad. I'll correct the previous post for clarity and apologies.
                  "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

                  Comment


                  • #10
                    Oh not a problem! Thanks for your help!!


                    At R41, I find the expected 15.4v but at the top of D14, i am getting -98v. I cant get to the Q20 as its under the heatsink. I also found the -100v at the top of D2, D3 and PIN3 of Q1.
                    Last edited by nickbme07; 08-30-2022, 03:31 AM.

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                    • #11
                      The schematic shows both 1/4" jacks paralleled, so if you have DC on one of the 1/4" jacks, you should have it on the other. This also corresponds to pin 1+ on the Neutrik connectors.
                      The other amp (high amp) is only accessible from pin 2+ on the Neutrik connectors (all referenced to ground). The high amp uses the LM3886. The main amp uses discreet components.
                      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                      • #12
                        Yes checking all 4 outputs, center pin all show -0.40mVdc from ground reference. No dc on PIN2 of Neutriks

                        Comment


                        • #13
                          When referring to diodes, call out anode and cathode rather than top or bottom, it will be more clear.
                          The red light is protect, blue is power. Your mute1 line is at -100V and no blue light. These both are determined by Q20, which gets it's command from U2 pin3. U2 responds to the 'fault' line coming into Q19, and also the thermal breaker S1 at Q18 base.
                          Originally posted by Enzo
                          I have a sign in my shop that says, "Never think up reasons not to check something."


                          Comment


                          • #14
                            The only preamp schematic I have is A3. It shows the blue light going to ground, so there is no place for -100V to be getting to D14.
                            Do you have all the boards in place with their grounds connected? If so, there may be a blown/burnt ground trace somewhere.
                            Or maybe a solder bridge or short between 2 traces that should not be there.
                            Originally posted by Enzo
                            I have a sign in my shop that says, "Never think up reasons not to check something."


                            Comment


                            • #15
                              No volts on S1, but it is shorted closed (if thats normal). Naturally Q19 and Q20 are under the heatsink. I am reading +1.2v on cathode and +0.6v for the D10 diode. On the D11 diode I see +0.6v on anode 0v on cathode.

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