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Crate Gremlins

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  • Crate Gremlins

    I have a Crate Gx-2200H (Excalibur) 220 watt SS head. What happens is the distortion channel (A, Gains 1&2) switches to clean channel (B) on it's own. When it does, signal is lost somehow. No output, no buzzing, no static, & no bueno. The amber Clean Channel LED will be lit though. As you may have guessed, a quick shot to the head would make it right. After awhile even that doesn't work.
    I have read quite a few threads here on the forum trying to get an idea what it may be.
    " A large proportion of problems with electronics generally are due to dirt in the wrong place."
    So I hosed the innards down with electronics cleaner, paying special attention to the channel select button..TINY switch..somekind of little blue square detent (?) switch.
    " the channel switching circuit runs THROUGH the FS jack, and those contacts complete the circuit when the jack is empty. SO if they get dirty, or their solder cracks as you found, as far as the amp is concerned it is the same as plugging in a foot switch an clicking the switch to open."
    And..
    " many Crate amps also have a footswitch jack that can have the same problem, only then it results in random channel switching...."
    But my amp will do it's goofy switching even with the footswitch plugged in.
    So I've come to think I may have to just start touching every doggone solder-joint on the board to try to eliminate any cold solders.
    I was thinking if there was a way to narrow it down, I would try. I can run a multimeter, read a schematic, and tin/solder electronics. I've never worked on an amp though.
    The best I could find on the web is an Owner's Manual, but it does give a good idead of the control layout and switches.
    I really like this amp and do not want to replace it. I've had it since 1996. Plus, I listened to too many Terry Date produced records as a kid, so it has the perfect metal tone for my ears when dialed in.
    Attached Files
    Last edited by twisted6buick; 10-20-2013, 10:34 PM.

  • #2
    "So I've come to think I may have to just start touching every doggone solder-joint on the board to try to eliminate any cold solders. "
    Not a bad idea.

    Comment


    • #3
      It is never a good idea to randomly resolder pc boards, you never will know if you fixed it or what the problem was if it temporarily resolves the issue. Random switching can be mechanical connections or intermittent electronics. If mechanical,, such as board connectors, jacks, or solder joints, you can cause the problem to occur by slight flexing the board, using a clean brush to sweep lightly over the various parts of the board, in tougher cases, using the bristles of an electric toothbrush or light tapping with an insulated prod.
      This should allow you to recreate the problem at will which is the first step in fixing a mechanical intermittent.

      Re-touching old oxidized solder is often worse than leaving it alone. The solder does not behave the same as new solder that has integrated flux and not oxidized so if you resort to such an ill-advised task of resoldering everything, remove the old solder completely from the joint, verify a solid mechanical connection( a proper solder joint will have low resistance without any solder applied) and use fresh solder. Reflowed solder never has as low of resistance and risks become a "cold" joint, which is very rare in equipment that has been working for a while. Most often, an intermittent connection is one where the solder is cracked and the lead is loose.
      If you isolate the defect to an area of the board, but can't see the broken joint, apply a little isopropyl alcohol to the area and shine some light on it. By looking at an angle, even minute movements of wire leads in what appears to be a good joint, can be seen by the interference patterns (ripples of reflected light) that develop when lightly touching various components from the component side of the board.
      If the problem is electronic, heat and cold can cause a failing part of act up. One you find a way to recreate the problem, it is very easy to trace down the circuit. Since it is going dead when the random switching occurs, it is not really switching, only part of the circuit is switching so no signal is routed fully through either signal path. Generally speaking in all amps, that can be a switching transistor for a single relay or a optical isolator in a circuit that requires several to work together to reroute the signal.
      Good luck.

      Comment


      • #4
        "tapping with an insulated prod"
        Tapped transistor at Q11. Fried Resistors at R11 and R21. Smoke. Glowing. ETC.
        Now it doesn't work at all.

        Comment


        • #5
          You are gonna need a schematic to work on this amp any further. Call Loud Technologies and give them the serial number model etc. They will make you agree to not share the schematic yadi yadi yadi... You probably can't tell what the value of the blown resistors are right? Yup call them tomorrow to get an emailed copy of the schematic.
          When the going gets weird... The weird turn pro!

          Comment


          • #6
            I was under the impression there was no Loud Technologies any longer.

            EDIT: sorry. No more CRATE. I found Loud's number. THX

            Comment


            • #7
              OK, I have all the relevant PDF's for the head.
              Here is a pic of the two resistors that fried at R11 and R21. In the top of the photo you can see the Transistor I made the mistake of tapping on. (Motorola MJ15001)
              Click image for larger version

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              I would guess that I need to replace these two resistors and get the head running again before I can fix the original problem? Or is this problem related to my first problem? I would guess that my first problem is in the Pre-amp board. The fried Resistors are just from me tapping on things that don't take too well to tapping with plastic implements. Correct? No?

              Comment


              • #8
                Originally posted by twisted6buick View Post
                The fried Resistors are just from me tapping on things that don't take too well to tapping with plastic implements. Correct? No?
                Unless you were tapping with a sledge hammer, I can't see why those resistors would burn.

                What do those resistors do? What are they connected to? Whatever they are connected to is the cause of the burning. If they are connected to a transistor and there is something loose from the board that could cause a current surge, burning the resistors.

                Comment


                • #9
                  Originally posted by 52 Bill View Post
                  Unless you were tapping with a sledge hammer....
                  Just a small mini-scewdriver handle.

                  Originally posted by 52 Bill View Post
                  What do those resistors do? What are they connected to?
                  I don't know anything. According to the diagram, there are Diodes between the Trans I tapped (Q11) and the two Res that popped (R11 & 21). The Diodes are D9 & D10.
                  Attached Files

                  Comment


                  • #10
                    You got your hands full with this one.
                    Tapping on the output transistor 'may' have caused it to short internally.
                    If it shorted Collector to base it may have damaged Q4, which took out R11 & 22.
                    Can you post the rest of the schematic?

                    Comment


                    • #11
                      Originally posted by Jazz P Bass View Post
                      ...it may have damaged Q4, which took out R11 & 22.
                      Is that Q4 in the photo with the winged heatsink? The case and heatsink are probably connected to the collector which could be near something that could have shorted when it was tapped.

                      Comment


                      • #12
                        Originally posted by Jazz P Bass View Post
                        Tapping on the output transistor 'may' have caused it to short internally.
                        If it shorted Collector to base it may have damaged Q4, which took out R11 & 22.
                        Can you post the rest of the schematic?
                        Yeah, internally. Sounds right. Q4 seems OK though. It didn't glow or smoke.

                        Originally posted by 52 Bill View Post
                        Is that Q4 in the photo with the winged heatsink? The case and heatsink are probably connected to the collector which could be near something that could have shorted when it was tapped.
                        Yes, Q4 has the odd heatsink. No it isn't- nor did it- touch anything.
                        Attached Files

                        Comment


                        • #13
                          OK, got out the two resistors and the transistor cleanly. The resistors seem to be 22 ohms and can be sourced from Radio Shack. I don't know if the are 1/4 watt or 1/2 watt though.
                          The transistor is a MJ15001 140v 200w that is hard to come by.

                          Any help once I get the power amp up and running again would be appreciated.

                          NOTE: Am I correct in thinking one board is the power amp and the other board is the pre amp? Also, the transistor is actually what powers the speakers?

                          Comment


                          • #14
                            So blown R11 & R21 both 22ohm resistors, easy fix. You said that you pulled out one of the output transistors...? Have you tested any of the outputs for shorts? You do have some sort of multimeter for testing? When dealing with rebuilding of a power amp circuit, it would be wise to have a light bulb limiter ready to go.
                            When the going gets weird... The weird turn pro!

                            Comment


                            • #15
                              Mouser lists MJ15001, but is out of stock. According to the web page for that part, they expect some in about December 19th.

                              SO if they don;t have them, use MJ15003 instead, those are common enough.
                              Last edited by Enzo; 10-25-2013, 04:28 AM. Reason: typos
                              Education is what you're left with after you have forgotten what you have learned.

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